Fix typos (#20417)

packages/flutter/lib/src/animation/animations.dart

@@ -369,7 +369,7 @@ class CurvedAnimation extends Animation<double> with AnimationWithParentMixin<do
   ///
   /// The curve direction is only reset when we hit the beginning or the end of
   /// the timeline to avoid discontinuities in the value of any variables this
-  /// a animation is used to animate.
+  /// animation is used to animate.
   AnimationStatus _curveDirection;
 
   void _updateCurveDirection(AnimationStatus status) {

packages/flutter/lib/src/foundation/serialization.dart

@@ -65,7 +65,7 @@ class WriteBuffer {
     _buffer.addAll(list);
   }
 
-  /// Write all the values from a [Int32List] into the buffer.
+  /// Write all the values from an [Int32List] into the buffer.
   void putInt32List(Int32List list) {
     _alignTo(4);
     _buffer.addAll(list.buffer.asUint8List(list.offsetInBytes, 4 * list.length));

packages/flutter/lib/src/material/material_localizations.dart

@@ -138,7 +138,7 @@ abstract class MaterialLocalizations {
   /// Label read out by accessibility tools (TalkBack or VoiceOver) for a modal
   /// barrier to indicate that a tap dismisses the barrier.
   ///
-  /// A modal barrier can for example be found behind a alert or popup to block
+  /// A modal barrier can for example be found behind an alert or popup to block
   /// user interaction with elements behind it.
   String get modalBarrierDismissLabel;
 

packages/flutter/lib/src/painting/alignment.dart

@@ -14,7 +14,7 @@ import 'basic_types.dart';
 /// A property or argument of this type accepts classes created either with [new
 /// Alignment] and its variants, or [new AlignmentDirectional].
 ///
-/// To convert a [AlignmentGeometry] object of indeterminate type into a
+/// To convert an [AlignmentGeometry] object of indeterminate type into an
 /// [Alignment] object, call the [resolve] method.
 @immutable
 abstract class AlignmentGeometry {
@@ -115,7 +115,7 @@ abstract class AlignmentGeometry {
     );
   }
 
-  /// Convert this instance into a [Alignment], which uses literal
+  /// Convert this instance into an [Alignment], which uses literal
   /// coordinates (the `x` coordinate being explicitly a distance from the
   /// left).
   ///
@@ -173,7 +173,7 @@ abstract class AlignmentGeometry {
 /// A variety of widgets use [Alignment] in their configuration, most
 /// notably:
 ///
-///  * [Align] positions a child according to a [Alignment].
+///  * [Align] positions a child according to an [Alignment].
 ///
 /// See also:
 ///
@@ -414,7 +414,7 @@ class AlignmentDirectional extends AlignmentGeometry {
   /// than -1.0 represent positions beyond the start edge, and values greater than
   /// 1.0 represent positions beyond the end edge.
   ///
-  /// This value is normalized into a [Alignment.x] value by the [resolve]
+  /// This value is normalized into an [Alignment.x] value by the [resolve]
   /// method.
   final double start;
 

packages/flutter/lib/src/painting/decoration_image.dart

@@ -71,7 +71,7 @@ class DecorationImage {
   /// How to align the image within its bounds.
   ///
   /// The alignment aligns the given position in the image to the given position
-  /// in the layout bounds. For example, a [Alignment] alignment of (-1.0,
+  /// in the layout bounds. For example, an [Alignment] alignment of (-1.0,
   /// -1.0) aligns the image to the top-left corner of its layout bounds, while a
   /// [Alignment] alignment of (1.0, 1.0) aligns the bottom right of the
   /// image with the bottom right corner of its layout bounds. Similarly, an

packages/flutter/lib/src/rendering/shifted_box.dart

@@ -267,7 +267,7 @@ abstract class RenderAligningShiftedBox extends RenderShiftedBox {
   /// For example, a value of 0.0 means that the center of the child is aligned
   /// with the center of the parent.
   ///
-  /// If this is set to a [AlignmentDirectional] object, then
+  /// If this is set to an [AlignmentDirectional] object, then
   /// [textDirection] must not be null.
   AlignmentGeometry get alignment => _alignment;
   AlignmentGeometry _alignment;
@@ -322,7 +322,7 @@ abstract class RenderAligningShiftedBox extends RenderShiftedBox {
   }
 }
 
-/// Positions its child using a [AlignmentGeometry].
+/// Positions its child using an [AlignmentGeometry].
 ///
 /// For example, to align a box at the bottom right, you would pass this box a
 /// tight constraint that is bigger than the child's natural size,

packages/flutter/lib/src/widgets/animated_list.dart

@@ -166,7 +166,7 @@ class AnimatedList extends StatefulWidget {
     if (nullOk || result != null)
       return result;
     throw new FlutterError(
-      'AnimatedList.of() called with a context that does not contain a AnimatedList.\n'
+      'AnimatedList.of() called with a context that does not contain an AnimatedList.\n'
       'No AnimatedList ancestor could be found starting from the context that was passed to AnimatedList.of(). '
       'This can happen when the context provided is from the same StatefulWidget that '
       'built the AnimatedList. Please see the AnimatedList documentation for examples '

packages/flutter/lib/src/widgets/fade_in_image.dart

@@ -242,8 +242,8 @@ class FadeInImage extends StatefulWidget {
   /// How to align the image within its bounds.
   ///
   /// The alignment aligns the given position in the image to the given position
-  /// in the layout bounds. For example, a [Alignment] alignment of (-1.0,
-  /// -1.0) aligns the image to the top-left corner of its layout bounds, while a
+  /// in the layout bounds. For example, an [Alignment] alignment of (-1.0,
+  /// -1.0) aligns the image to the top-left corner of its layout bounds, while an
   /// [Alignment] alignment of (1.0, 1.0) aligns the bottom right of the
   /// image with the bottom right corner of its layout bounds. Similarly, an
   /// alignment of (0.0, 1.0) aligns the bottom middle of the image with the

packages/flutter/lib/src/widgets/framework.dart

@@ -4025,7 +4025,7 @@ class ParentDataElement<T extends RenderObjectWidget> extends ProxyElement {
   }
 }
 
-/// An [Element] that uses a [InheritedWidget] as its configuration.
+/// An [Element] that uses an [InheritedWidget] as its configuration.
 class InheritedElement extends ProxyElement {
   /// Creates an element that uses the given widget as its configuration.
   InheritedElement(InheritedWidget widget) : super(widget);

packages/flutter/lib/src/widgets/image.dart

@@ -456,8 +456,8 @@ class Image extends StatefulWidget {
   /// How to align the image within its bounds.
   ///
   /// The alignment aligns the given position in the image to the given position
-  /// in the layout bounds. For example, a [Alignment] alignment of (-1.0,
-  /// -1.0) aligns the image to the top-left corner of its layout bounds, while a
+  /// in the layout bounds. For example, an [Alignment] alignment of (-1.0,
+  /// -1.0) aligns the image to the top-left corner of its layout bounds, while an
   /// [Alignment] alignment of (1.0, 1.0) aligns the bottom right of the
   /// image with the bottom right corner of its layout bounds. Similarly, an
   /// alignment of (0.0, 1.0) aligns the bottom middle of the image with the

packages/flutter/lib/src/widgets/localizations.dart

@@ -187,10 +187,10 @@ class _WidgetsLocalizationsDelegate extends LocalizationsDelegate<WidgetsLocaliz
 ///
 /// See also:
 ///
-///  * [GlobalWidgetsLocalizations], which provides widgets localizations for
-///    many languages.
-///  * [WidgetsApp.delegates], which automatically includes
-///    [DefaultWidgetsLocalizations.delegate] by default.
+/// * [GlobalWidgetsLocalizations], which provides widgets localizations for
+///   many languages.
+/// * [WidgetsApp.delegates], which automatically includes
+///   [DefaultWidgetsLocalizations.delegate] by default.
 class DefaultWidgetsLocalizations implements WidgetsLocalizations {
   /// Construct an object that defines the localized values for the widgets
   /// library for US English (only).
@@ -257,9 +257,9 @@ class _LocalizationsScope extends InheritedWidget {
 ///   @override
 ///   Future<MyLocalizations> load(Locale locale) => MyLocalizations.load(locale);
 ///
-///  @override
-///  bool shouldReload(MyLocalizationsDelegate old) => false;
-///}
+///   @override
+///   bool shouldReload(MyLocalizationsDelegate old) => false;
+/// }
 /// ```
 ///
 /// Each delegate can be viewed as a factory for objects that encapsulate a