cc: Add support for partial swaps when using impl-side painting.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 4a945a224384de89251c3b1d7a2b888f932c4999..fb6926e40367822690141eaaa15d19a50315065d 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1212,9 +1212,6 @@ void LayerTreeHostImpl::DidModifyTilePriorities() {
 }
 
 void LayerTreeHostImpl::DidInitializeVisibleTile() {
-  // TODO(reveman): Determine tiles that changed and only damage
-  // what's necessary.
-  SetFullRootLayerDamage();
   if (client_ && !client_->IsInsideDraw())
     client_->DidInitializeVisibleTileOnImplThread();
 }
@@ -1223,6 +1220,19 @@ void LayerTreeHostImpl::NotifyReadyToActivate() {
   client_->NotifyReadyToActivate();
 }
 
+void LayerTreeHostImpl::NotifyTileInitialized(const Tile* tile) {
+  if (!active_tree_)
+    return;
+
+  LayerImpl* layer_impl =
+      active_tree_->FindActiveTreeLayerById(tile->layer_id());
+  if (layer_impl) {
+    gfx::RectF tile_in_layer_content_rect =

[reveman, 2014/04/15 16:25:59]

is this supposed to be tile_content_rect_in_layer_space?

[enne (OOO), 2014/04/15 17:27:27]

I think this should just be called layer_rect or layer_damage_rect.

+        gfx::ScaleRect(tile->content_rect(), 1 / tile->contents_scale());

[enne (OOO), 2014/04/15 17:27:27]

nit: 1 => 1.f

+    layer_impl->UnionDamageContentRect(tile_in_layer_content_rect);

[enne (OOO), 2014/04/15 17:27:27]

This function seems misnamed.  It should be UnionDamageLayerRect and not
content.

+  }
+}
+
 void LayerTreeHostImpl::SetMemoryPolicy(const ManagedMemoryPolicy& policy) {
   SetManagedMemoryPolicy(policy, zero_budget_);
 }