Avoid heap allocations with GestureEventDataPacket

ui/events/gesture_detection/gesture_event_data_packet.h

 // 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_GESTURE_EVENT_DATA_PACKET_H_
 #define UI_EVENTS_GESTURE_DETECTION_GESTURE_EVENT_DATA_PACKET_H_
 
-#include <vector>
-
+#include "base/containers/stack_container.h"
 #include "ui/events/gesture_detection/gesture_detection_export.h"
 #include "ui/events/gesture_detection/gesture_event_data.h"
 
 namespace ui {
 
 class MotionEvent;
 
 // Acts as a transport container for gestures created (directly or indirectly)
 // by a touch event.
 class GESTURE_DETECTION_EXPORT GestureEventDataPacket {
@@ skipping 17 matching lines @@
 
   // Factory methods for creating a packet from a particular event.
   static GestureEventDataPacket FromTouch(const ui::MotionEvent& touch);
   static GestureEventDataPacket FromTouchTimeout(
       const GestureEventData& gesture);
 
   void Push(const GestureEventData& gesture);
 
   const base::TimeTicks& timestamp() const { return timestamp_; }
   const GestureEventData& gesture(size_t i) const { return gestures_[i]; }
-  size_t gesture_count() const { return gestures_.size(); }
+  size_t gesture_count() const { return gestures_->size(); }
   GestureSource gesture_source() const { return gesture_source_; }
   const gfx::PointF& touch_location() const { return touch_location_; }
   const gfx::PointF& raw_touch_location() const { return raw_touch_location_; }
 
  private:
   GestureEventDataPacket(base::TimeTicks timestamp,
                          GestureSource source,
                          const gfx::PointF& touch_location,
                          const gfx::PointF& raw_touch_location);
 
+  enum { kTypicalMaxGesturesPerTouch = 5 };
   base::TimeTicks timestamp_;
-  // TODO(jdduke): This vector is in general very short. Optimize?
-  std::vector<GestureEventData> gestures_;
+  base::StackVector<GestureEventData, kTypicalMaxGesturesPerTouch> gestures_;
   gfx::PointF touch_location_;
   gfx::PointF raw_touch_location_;
   GestureSource gesture_source_;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_GESTURE_DETECTION_GESTURE_EVENT_DATA_PACKET_H_