Just-in-time mutations of GestureDetector

This allows us to adjust exactly which gestures we're listening for
during layout, which I'll use to kill a SizeObserver.

examples/material_gallery/android/AndroidManifest.xml

@@ -6,6 +6,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="io.flutter.MaterialGallery" android:versionCode="1" android:versionName="0.0.1">
 
     <uses-sdk android:minSdkVersion="14" android:targetSdkVersion="21" />
+    <uses-permission android:name="android.permission.INTERNET"/>
 
     <application android:icon="@mipmap/ic_launcher" android:label="Flutter Material" android:name="org.domokit.sky.shell.SkyApplication">
         <activity android:configChanges="orientation|keyboardHidden|keyboard|screenSize" android:hardwareAccelerated="true" android:launchMode="singleTask" android:name="org.domokit.sky.shell.SkyActivity" android:theme="@android:style/Theme.Black.NoTitleBar">

packages/flutter/lib/src/gestures/drag.dart

@@ -143,6 +143,8 @@ class VerticalDragGestureRecognizer extends _DragGestureRecognizer<double> {
   double get _initialPendingDragDelta => 0.0;
   double _getDragDelta(PointerEvent event) => event.delta.dy;
   bool get _hasSufficientPendingDragDeltaToAccept => _pendingDragDelta.abs() > kTouchSlop;
+
+  String toStringShort() => 'vertical drag';
 }
 
 class HorizontalDragGestureRecognizer extends _DragGestureRecognizer<double> {
@@ -163,6 +165,8 @@ class HorizontalDragGestureRecognizer extends _DragGestureRecognizer<double> {
   double get _initialPendingDragDelta => 0.0;
   double _getDragDelta(PointerEvent event) => event.delta.dx;
   bool get _hasSufficientPendingDragDeltaToAccept => _pendingDragDelta.abs() > kTouchSlop;
+
+  String toStringShort() => 'horizontal drag';
 }
 
 class PanGestureRecognizer extends _DragGestureRecognizer<Offset> {
@@ -185,4 +189,6 @@ class PanGestureRecognizer extends _DragGestureRecognizer<Offset> {
   bool get _hasSufficientPendingDragDeltaToAccept {
     return _pendingDragDelta.distance > kPanSlop;
   }
+
+  String toStringShort() => 'pan';
 }

packages/flutter/lib/src/gestures/long_press.dart

@@ -34,4 +34,6 @@ class LongPressGestureRecognizer extends PrimaryPointerGestureRecognizer {
     if (event is PointerUpEvent)
       resolve(GestureDisposition.rejected);
   }
+
+  String toStringShort() => 'long press';
 }

packages/flutter/lib/src/gestures/multidrag.dart

@@ -250,6 +250,8 @@ class ImmediateMultiDragGestureRecognizer extends MultiDragGestureRecognizer<_Im
   _ImmediatePointerState createNewPointerState(PointerDownEvent event) {
     return new _ImmediatePointerState(event.position);
   }
+
+  String toStringShort() => 'multidrag';
 }
 
 
@@ -277,6 +279,8 @@ class HorizontalMultiDragGestureRecognizer extends MultiDragGestureRecognizer<_H
   _HorizontalPointerState createNewPointerState(PointerDownEvent event) {
     return new _HorizontalPointerState(event.position);
   }
+
+  String toStringShort() => 'horizontal multidrag';
 }
 
 
@@ -304,6 +308,8 @@ class VerticalMultiDragGestureRecognizer extends MultiDragGestureRecognizer<_Ver
   _VerticalPointerState createNewPointerState(PointerDownEvent event) {
     return new _VerticalPointerState(event.position);
   }
+
+  String toStringShort() => 'vertical multidrag';
 }
 
 
@@ -373,4 +379,6 @@ class DelayedMultiDragGestureRecognizer extends MultiDragGestureRecognizer<_Dela
   _DelayedPointerState createNewPointerState(PointerDownEvent event) {
     return new _DelayedPointerState(event.position, _delay);
   }
+
+  String toStringShort() => 'long multidrag';
 }

packages/flutter/lib/src/gestures/multitap.dart

@@ -212,6 +212,7 @@ class DoubleTapGestureRecognizer extends GestureRecognizer {
     }
   }
 
+  String toStringShort() => 'double tap';
 }
 
 
@@ -385,4 +386,5 @@ class MultiTapGestureRecognizer extends GestureRecognizer {
     _gestureArena = null;
   }
 
+  String toStringShort() => 'multitap';
 }

packages/flutter/lib/src/gestures/recognizer.dart

@@ -42,6 +42,9 @@ abstract class GestureRecognizer extends GestureArenaMember {
   /// GestureDetector widget calls this method).
   void dispose() { }
 
+  /// Returns a very short pretty description of the gesture that the
+  /// recognizer looks for, like 'tap' or 'horizontal drag'.
+  String toStringShort() => toString();
 }
 
 /// Base class for gesture recognizers that can only recognize one

packages/flutter/lib/src/gestures/scale.dart

@@ -135,4 +135,6 @@ class ScaleGestureRecognizer extends OneSequenceGestureRecognizer {
     }
     _state = ScaleState.ready;
   }
+
+  String toStringShort() => 'scale';
 }

packages/flutter/lib/src/gestures/tap.dart

@@ -102,4 +102,6 @@ class TapGestureRecognizer extends PrimaryPointerGestureRecognizer {
     _wonArena = false;
     _finalPosition = null;
   }
+
+  String toStringShort() => 'tap';
 }