Clamp invalidation regions of PictureLayer to layer bounds

Clamps the incoming invalidation regions of PictureLayer to the actual layer bounds to avoid bloating the update region data structure. It also adds an early out when the invalidation rect is empty. 

Review URL: https://chromiumcodereview.appspot.com/11824013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@175952 0039d316-1c4b-4281-b951-d872f2087c98

cc/picture_layer.cc

@@ -51,7 +51,11 @@ void PictureLayer::setLayerTreeHost(LayerTreeHost* host) {
 
 void PictureLayer::setNeedsDisplayRect(const gfx::RectF& layer_rect) {
   gfx::Rect rect = gfx::ToEnclosedRect(layer_rect);
-  pending_invalidation_.Union(rect);
+  if (!rect.IsEmpty()) {
+    // Clamp invalidation to the layer bounds.
+    rect.Intersect(gfx::Rect(bounds()));
+    pending_invalidation_.Union(rect);
+  }
   Layer::setNeedsDisplayRect(layer_rect);
 }