cc: Only allow trees created at the current viewport size to draw.

cc/layer_tree_impl.cc

Index: cc/layer_tree_impl.cc
diff --git a/cc/layer_tree_impl.cc b/cc/layer_tree_impl.cc
index 38a40f315cab2288e0fa14718754aad2427e8ec2..1b92a65f27f1edac7b74e40ee632da55cb3cf72b 100644
--- a/cc/layer_tree_impl.cc
+++ b/cc/layer_tree_impl.cc
@@ -92,6 +92,7 @@ void LayerTreeImpl::pushPropertiesTo(LayerTreeImpl* target_tree) {
   target_tree->SetPageScaleDelta(
       target_tree->page_scale_delta() / target_tree->sent_page_scale_delta());
   target_tree->set_sent_page_scale_delta(1);
+  target_tree->SetViewportSize(layout_viewport_size_, device_viewport_size_);
 
   // This should match the property synchronization in
   // LayerTreeHost::finishCommitOnImplThread().
@@ -269,6 +270,23 @@ void LayerTreeImpl::ClearRenderSurfaces() {
   set_needs_update_draw_properties();
 }
 
+void LayerTreeImpl::SetViewportSize(gfx::Size layout_viewport_size,
+                                    gfx::Size device_viewport_size) {
+    if (device_viewport_size_ == device_viewport_size &&

[danakj, 2013/02/13 08:19:54]

sorry, but 2 space indent here :|

+        layout_viewport_size_ == layout_viewport_size)
+        return;
+
+    layout_viewport_size_ = layout_viewport_size;
+    device_viewport_size_ = device_viewport_size;
+
+    UpdateMaxScrollOffset();
+
+    if (IsActiveTree() && layer_tree_host_impl_->renderer())
+        layer_tree_host_impl_->renderer()->viewportChanged();
+
+    layer_tree_host_impl_->OnCanDrawStateChangedForTree(this);
+}
+
 bool LayerTreeImpl::AreVisibleResourcesReady() const {
   TRACE_EVENT0("cc", "LayerTreeImpl::AreVisibleResourcesReady");
 
@@ -428,14 +446,6 @@ float LayerTreeImpl::device_scale_factor() const {
   return layer_tree_host_impl_->deviceScaleFactor();
 }
 
-const gfx::Size& LayerTreeImpl::device_viewport_size() const {
-  return layer_tree_host_impl_->deviceViewportSize();
-}
-
-const gfx::Size& LayerTreeImpl::layout_viewport_size() const {
-  return layer_tree_host_impl_->layoutViewportSize();
-}
-
 std::string LayerTreeImpl::layer_tree_as_text() const {
   return layer_tree_host_impl_->layerTreeAsText();
 }