android webview: allow cc to fail hardware draw

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 6b0c9fd2e0549a1bb3532a8695fb8ce872ac2865..6d94f41ee71fadd901759ffdb5bbdce706f8fb0b 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -1092,10 +1092,10 @@ void LayerTreeImpl::AsValueInto(base::trace_event::TracedValue* state) const {
   state->EndArray();
 }
 
-void LayerTreeImpl::DistributeRootScrollOffset(
+bool LayerTreeImpl::DistributeRootScrollOffset(
     const gfx::ScrollOffset& root_offset) {
   if (!InnerViewportScrollLayer())
-    return;
+    return false;
 
   DCHECK(OuterViewportScrollLayer());
 
@@ -1109,7 +1109,7 @@ void LayerTreeImpl::DistributeRootScrollOffset(
   // It may be nothing has changed.
   DCHECK(inner_viewport_offset + outer_viewport_offset == TotalScrollOffset());
   if (inner_viewport_offset + outer_viewport_offset == root_offset)
-    return;
+    return false;
 
   gfx::ScrollOffset max_outer_viewport_scroll_offset =
       OuterViewportScrollLayer()->MaxScrollOffset();
@@ -1121,6 +1121,7 @@ void LayerTreeImpl::DistributeRootScrollOffset(
   OuterViewportScrollLayer()->SetCurrentScrollOffset(outer_viewport_offset);
   inner_viewport_offset = root_offset - outer_viewport_offset;
   InnerViewportScrollLayer()->SetCurrentScrollOffset(inner_viewport_offset);
+  return true;
 }
 
 void LayerTreeImpl::QueueSwapPromise(scoped_ptr<SwapPromise> swap_promise) {