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 2faa6b2849543c5d7e0ed20a9e3b9a1f2674a5ab..161ed8f243226b6c76a1d58f61d4e0f558942366 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1194,9 +1194,6 @@ 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();
 }
@@ -1205,6 +1202,15 @@ void LayerTreeHostImpl::NotifyReadyToActivate() {
   client_->NotifyReadyToActivate();
 }
 
+void LayerTreeHostImpl::NotifyInitializedTiles(Tile* tile) {
+  LayerImpl* layer_impl = NULL;

[reveman, 2014/04/14 20:03:07]

nit: move to where it's first used instead

[sohanjg, 2014/04/15 10:03:48]

Done.

+  if (active_tree_) {

[reveman, 2014/04/14 20:03:07]

nit: maybe cleaner to early out instead of having nested if statements

[sohanjg, 2014/04/15 10:03:48]

Done.

+    layer_impl = active_tree_->FindActiveTreeLayerById(tile->layer_id());
+    if (layer_impl)
+      layer_impl->UnionDamageRect(tile->content_rect());

[danakj, 2014/04/14 17:17:07]

The tile's content rect is in the tiling's content space, which is not the same
thing as the layer's content space. If you scale it by the tile's tiling's
content scale, you'll get back to layer space.

So something like tile->content_rect() * / tiling_content_scale_{x,y} would give
you a rect in the layer's content space. You probably want this rect as floats,
like update_rect_ since each pixel there may be many physical pixels.

[sohanjg, 2014/04/15 10:03:48]

Done.

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