cc: Force an update on tile size after viewport resize

cc/layers/picture_layer_impl.h

Index: cc/layers/picture_layer_impl.h
diff --git a/cc/layers/picture_layer_impl.h b/cc/layers/picture_layer_impl.h
index 397cb623bbd0e82428799117c980d41dcdea18b0..2bb0ee360433c418572d3ea78ff2c9b4e092880e 100644
--- a/cc/layers/picture_layer_impl.h
+++ b/cc/layers/picture_layer_impl.h
@@ -171,6 +171,10 @@ class CC_EXPORT PictureLayerImpl
   gfx::Rect visible_rect_for_tile_priority_;
   gfx::Rect viewport_rect_for_tile_priority_in_content_space_;
 
+  // Keep track of the last viewport rect. If it changes, we need to ensure that
+  // the texture size is correct in the tiling.
+  gfx::Size last_viewport_size_;
+
   // List of tilings that were used last time we appended quads. This can be
   // used as an optimization not to remove tilings if they are still being
   // drawn. Note that accessing this vector should only be done in the context