views: Stop dispatching scroll-gesture events if the scroll-begin event wasn't handled.

ui/views/widget/root_view.cc

 // Copyright (c) 2012 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.
 
 #include "ui/views/widget/root_view.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "base/message_loop.h"
@@ skipping 270 matching lines @@
           event->SetHandled();
           return;
         }
       }
       scroll_gesture_handler_ = NULL;
     }
 
     return;
   }
 
+  // If there was no handler for a SCROLL_BEGIN event, then subsequent scroll
+  // events are not dispatched to any views.
+  switch (event->type()) {
+    case ui::ET_GESTURE_SCROLL_UPDATE:
+    case ui::ET_GESTURE_SCROLL_END:
+    case ui::ET_SCROLL_FLING_START:
+      return;
+    default:
+      break;
+  }
+
   // Walk up the tree until we find a view that wants the gesture event.
   for (gesture_handler_ = GetEventHandlerForPoint(event->location());
       gesture_handler_ && (gesture_handler_ != this);
       gesture_handler_ = gesture_handler_->parent()) {
     if (!gesture_handler_->enabled()) {
       // Disabled views eat events but are treated as not handled.
       return;
     }
 
     // See if this view wants to handle the Gesture.
@@ skipping 350 matching lines @@
 }
 
 void RootView::SetMouseLocationAndFlags(const ui::MouseEvent& event) {
   last_mouse_event_flags_ = event.flags();
   last_mouse_event_x_ = event.x();
   last_mouse_event_y_ = event.y();
 }
 
 }  // namespace internal
 }  // namespace views