Suppress scrolls that begin on fixed-pos layers.

content/renderer/gpu/input_handler_proxy.cc

Index: content/renderer/gpu/input_handler_proxy.cc
diff --git a/content/renderer/gpu/input_handler_proxy.cc b/content/renderer/gpu/input_handler_proxy.cc
index 77dd0f0af8472559f704120c5ad6618f4c2ec418..e81ebf0227d6d60a6fe218ce9676afc0ac0f9663 100644
--- a/content/renderer/gpu/input_handler_proxy.cc
+++ b/content/renderer/gpu/input_handler_proxy.cc
@@ -60,6 +60,7 @@ InputHandlerProxy::InputHandlerProxy(cc::InputHandler* input_handler)
       expect_pinch_update_end_(false),
 #endif
       gesture_scroll_on_impl_thread_(false),
+      gesture_scroll_on_main_thread_(false),
       gesture_pinch_on_impl_thread_(false),
       fling_may_be_active_on_main_thread_(false),
       fling_overscrolled_horizontally_(false),
@@ -150,6 +151,7 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::HandleInputEvent(
         gesture_scroll_on_impl_thread_ = true;
         return DID_HANDLE;
       case cc::InputHandler::ScrollOnMainThread:
+        gesture_scroll_on_main_thread_ = true;
         return DID_NOT_HANDLE;
       case cc::InputHandler::ScrollIgnored:
         return DROP_EVENT;
@@ -159,9 +161,12 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::HandleInputEvent(
     DCHECK(expect_scroll_update_end_);
 #endif
 
-    if (!gesture_scroll_on_impl_thread_ && !gesture_pinch_on_impl_thread_)
+    if (gesture_scroll_on_main_thread_)
       return DID_NOT_HANDLE;
 
+    if (!gesture_scroll_on_impl_thread_ && !gesture_pinch_on_impl_thread_)
+      return DROP_EVENT;
+
     const WebGestureEvent& gesture_event =
         *static_cast<const WebGestureEvent*>(&event);
     bool did_scroll = input_handler_->ScrollBy(
@@ -176,8 +181,13 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::HandleInputEvent(
 #endif
     input_handler_->ScrollEnd();
 
-    if (!gesture_scroll_on_impl_thread_)
+    if (gesture_scroll_on_main_thread_) {
+      gesture_scroll_on_main_thread_ = false;
       return DID_NOT_HANDLE;
+    }
+
+    if (!gesture_scroll_on_impl_thread_)
+      return DROP_EVENT;
 
     gesture_scroll_on_impl_thread_ = false;
     return DID_HANDLE;
@@ -244,7 +254,7 @@ InputHandlerProxy::HandleGestureFling(
         gfx::Point(gesture_event.x, gesture_event.y),
         cc::InputHandler::NonBubblingGesture);
   } else {
-    if (!gesture_scroll_on_impl_thread_)
+    if (gesture_scroll_on_main_thread_)
       scroll_status = cc::InputHandler::ScrollOnMainThread;
     else
       scroll_status = input_handler_->FlingScrollBegin();