Fix missing fields in GestureScrollBegin/Update/End event conversions.

third_party/WebKit/Source/platform/PlatformGestureEvent.h

Index: third_party/WebKit/Source/platform/PlatformGestureEvent.h
diff --git a/third_party/WebKit/Source/platform/PlatformGestureEvent.h b/third_party/WebKit/Source/platform/PlatformGestureEvent.h
index 350fe9ebdbd0a19cecd856d2b4ab704d5a16f2f8..86ec241bc832c00b2541a01bb2868429e52a5aaf 100644
--- a/third_party/WebKit/Source/platform/PlatformGestureEvent.h
+++ b/third_party/WebKit/Source/platform/PlatformGestureEvent.h
@@ -99,19 +99,19 @@ public:
 
     float deltaX() const
     {
-        ASSERT(m_type == PlatformEvent::GestureScrollUpdate);
+        ASSERT(m_type == PlatformEvent::GestureScrollBegin || m_type == PlatformEvent::GestureScrollUpdate);
         return m_data.m_scroll.m_deltaX;
     }
 
     float deltaY() const
     {
-        ASSERT(m_type == PlatformEvent::GestureScrollUpdate);
+        ASSERT(m_type == PlatformEvent::GestureScrollBegin || m_type == PlatformEvent::GestureScrollUpdate);
         return m_data.m_scroll.m_deltaY;
     }
 
     ScrollGranularity deltaUnits() const
     {
-        ASSERT(m_type == PlatformEvent::GestureScrollUpdate);
+        ASSERT(m_type == PlatformEvent::GestureScrollBegin || m_type == PlatformEvent::GestureScrollUpdate || m_type == PlatformEvent::GestureScrollEnd);
         return m_data.m_scroll.m_deltaUnits;
     }
 
@@ -135,10 +135,16 @@ public:
 
     bool inertial() const
     {
-        ASSERT(m_type == PlatformEvent::GestureScrollUpdate || m_type == PlatformEvent::GestureScrollEnd);
+        ASSERT(m_type == PlatformEvent::GestureScrollBegin || m_type == PlatformEvent::GestureScrollUpdate || m_type == PlatformEvent::GestureScrollEnd);
         return m_data.m_scroll.m_inertial;
     }
 
+    bool synthetic() const
+    {
+        ASSERT(m_type == PlatformEvent::GestureScrollBegin || m_type == PlatformEvent::GestureScrollEnd);
+        return m_data.m_scroll.m_synthetic;
+    }
+
     int resendingPluginId() const
     {
         if (m_type == PlatformEvent::GestureScrollUpdate
@@ -214,6 +220,8 @@ protected:
         } m_tap;
 
         struct {
+            // |m_deltaX| and |m_deltaY| represent deltas in GSU but
+            // are only hints in GSB.
             float m_deltaX;
             float m_deltaY;
             float m_velocityX;
@@ -222,6 +230,7 @@ protected:
             bool m_inertial;
             ScrollGranularity m_deltaUnits;
             int m_resendingPluginId;
+            bool m_synthetic;
         } m_scroll;
 
         struct {