Remove IconThemeData.clampedOpacity (#3483)

* Remove IconThemeData.clampedOpacity

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

@@ -191,7 +191,7 @@ class AppBar extends StatelessWidget {
 
       if (iconTheme != null) {
         iconTheme = new IconThemeData(
-          opacity: opacity * iconTheme.clampedOpacity,
+          opacity: opacity * iconTheme.opacity,
           color: iconTheme.color
         );
       }

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

@@ -76,7 +76,7 @@ class Icon extends StatelessWidget {
     if (icon == null)
       return new SizedBox(width: size, height: size);
 
-    final double iconOpacity = IconTheme.of(context)?.clampedOpacity ?? 1.0;
+    final double iconOpacity = IconTheme.of(context)?.opacity ?? 1.0;
     Color iconColor = color ?? _getDefaultColor(context);
     if (iconOpacity != 1.0)
       iconColor = iconColor.withOpacity(iconColor.opacity * iconOpacity);

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

@@ -12,23 +12,22 @@ import 'dart:ui' show Color, hashValues;
 class IconThemeData {
   /// Creates an icon theme data.
   ///
-  /// The given opacity applies to both explicit and default icon colors.
-  const IconThemeData({ this.color, this.opacity });
+  /// The opacity applies to both explicit and default icon colors. The value
+  /// is clamped between 0.0 and 1.0.
+  const IconThemeData({ this.color, double opacity: 1.0 }) : _opacity = opacity;
 
   /// The default color for icons.
   final Color color;
 
   /// An opacity to apply to both explicit and default icon colors.
-  final double opacity;
-
-  /// Normalizes the given opacity to be between 0.0 and 1.0 (inclusive).
-  double get clampedOpacity => (opacity ?? 1.0).clamp(0.0, 1.0);
+  double get opacity => (_opacity ?? 1.0).clamp(0.0, 1.0);
+  final double _opacity;
 
   /// Linearly interpolate between two icon theme data objects.
   static IconThemeData lerp(IconThemeData begin, IconThemeData end, double t) {
     return new IconThemeData(
       color: Color.lerp(begin.color, end.color, t),
-      opacity: ui.lerpDouble(begin.clampedOpacity, end.clampedOpacity, t)
+      opacity: ui.lerpDouble(begin.opacity, end.opacity, t)
     );
   }
 

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

@@ -96,6 +96,7 @@ class _PopupMenuItemState<T extends PopupMenuItem<dynamic>> extends State<T> {
       duration: kThemeChangeDuration,
       child: new Baseline(
         baseline: config.height - _kBaselineOffsetFromBottom,
+        baselineType: TextBaseline.alphabetic,
         child: buildChild()
       )
     );