Make GestureTextSelector detect its own gestures

ui/events/gesture_detection/scale_gesture_listeners.h

Index: ui/events/gesture_detection/scale_gesture_listeners.h
diff --git a/ui/events/gesture_detection/scale_gesture_listeners.h b/ui/events/gesture_detection/scale_gesture_listeners.h
new file mode 100644
index 0000000000000000000000000000000000000000..583ef7ea06e4ba20addc1a7788c52a3a5bea0fdf
--- /dev/null
+++ b/ui/events/gesture_detection/scale_gesture_listeners.h
@@ -0,0 +1,47 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_EVENTS_GESTURE_DETECTION_SCALE_GESTURE_LISTENERS_H_
+#define UI_EVENTS_GESTURE_DETECTION_SCALE_GESTURE_LISTENERS_H_
+
+#include "ui/events/gesture_detection/gesture_detection_export.h"
+
+namespace ui {
+
+class MotionEvent;
+class ScaleGestureDetector;
+
+// Client through which |ScaleGestureDetector| signals scale detection.
+class GESTURE_DETECTION_EXPORT ScaleGestureListener {
+ public:
+  virtual ~ScaleGestureListener() {}
+  virtual bool OnScale(const ScaleGestureDetector& detector,
+                       const MotionEvent& e) = 0;
+  virtual bool OnScaleBegin(const ScaleGestureDetector& detector,
+                            const MotionEvent& e) = 0;
+  virtual void OnScaleEnd(const ScaleGestureDetector& detector,
+                          const MotionEvent& e) = 0;
+};
+
+// A convenience class to extend when you only want to listen for a subset of
+// scaling-related events. This implements all methods in
+// |ScaleGestureListener| but does nothing.
+// |OnScale()| returns false so that a subclass can retrieve the accumulated
+// scale factor in an overridden |OnScaleEnd()|.
+// |OnScaleBegin() returns true.
+class GESTURE_DETECTION_EXPORT SimpleScaleGestureListener
+    : public ScaleGestureListener {
+ public:
+  // ScaleGestureListener implementation.
+  virtual bool OnScale(const ScaleGestureDetector&,
+                       const MotionEvent&) override;
+  virtual bool OnScaleBegin(const ScaleGestureDetector&,
+                            const MotionEvent&) override;
+  virtual void OnScaleEnd(const ScaleGestureDetector&,
+                          const MotionEvent&) override;
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_GESTURE_DETECTION_SCALE_GESTURE_LISTENERS_H_