cc: Allow the main thread to cancel commits

cc/layers/layer_impl.cc

 // Copyright 2011 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 "cc/layers/layer_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "base/strings/stringprintf.h"
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/scrollbar_animation_controller.h"
@@ skipping 247 matching lines @@
 }
 
 gfx::Vector2dF LayerImpl::ScrollBy(gfx::Vector2dF scroll) {
   gfx::Vector2dF min_delta = -scroll_offset_;
   gfx::Vector2dF max_delta = max_scroll_offset_ - scroll_offset_;
   // Clamp new_delta so that position + delta stays within scroll bounds.
   gfx::Vector2dF new_delta = (ScrollDelta() + scroll);
   new_delta.SetToMax(min_delta);
   new_delta.SetToMin(max_delta);
   gfx::Vector2dF unscrolled = ScrollDelta() + scroll - new_delta;
-
   SetScrollDelta(new_delta);
   return unscrolled;
 }
 
+void LayerImpl::ApplySentScrollDeltas() {
+  // Pending tree never has sent scroll deltas
+  DCHECK(layer_tree_impl()->IsActiveTree());
+
+  // Apply sent scroll deltas to scroll position / scroll delta as if the
+  // main thread had applied them and then committed those values.
+  //
+  // This function should not change the total scroll offset; it just shifts
+  // some of the scroll delta to the scroll offset.  Therefore, adjust these
+  // variables directly rather than calling the scroll offset delegate to
+  // avoid sending it multiple spurious calls.
+  //
+  // Because of the way scroll delta is calculated with a delegate, this will
+  // leave the total scroll offset unchanged on this layer regardless of
+  // whether a delegate is being used.
+  scroll_offset_ += sent_scroll_delta_;
+  scroll_delta_ -= sent_scroll_delta_;
+  sent_scroll_delta_ = gfx::Vector2d();
+}
+
 InputHandler::ScrollStatus LayerImpl::TryScroll(
     gfx::PointF screen_space_point,
     InputHandler::ScrollInputType type) const {
   if (should_scroll_on_main_thread()) {
     TRACE_EVENT0("cc", "LayerImpl::TryScroll: Failed ShouldScrollOnMainThread");
     return InputHandler::ScrollOnMainThread;
   }
 
   if (!screen_space_transform().IsInvertible()) {
     TRACE_EVENT0("cc", "LayerImpl::TryScroll: Ignored NonInvertibleTransform");
@@ skipping 603 matching lines @@
       pending_twin->SetScrollDelta(scroll_delta - sent_scroll_delta());
     }
   }
 
   if (scroll_offset_delegate_) {
     scroll_offset_delegate_->SetTotalScrollOffset(
         scroll_offset_ + scroll_delta);
   } else {
     scroll_delta_ = scroll_delta;
   }
+
   NoteLayerPropertyChangedForSubtree();
-
   UpdateScrollbarPositions();
 }
 
 gfx::Vector2dF LayerImpl::TotalScrollOffset() const {
   return scroll_offset_ + ScrollDelta();
 }
 
 void LayerImpl::SetDoubleSided(bool double_sided) {
   if (double_sided_ == double_sided)
     return;
@@ skipping 211 matching lines @@
 
 size_t LayerImpl::GPUMemoryUsageInBytes() const { return 0; }
 
 scoped_ptr<base::Value> LayerImpl::AsValue() const {
   scoped_ptr<base::DictionaryValue> state(new base::DictionaryValue());
   AsValueInto(state.get());
   return state.PassAs<base::Value>();
 }
 
 }  // namespace cc