ui/cc minor doc updates

Updates ui::Layer::SetMasksToBounds() to indicate masking also applies to
this layer.

Updates how_to reference in cc/README.md to point to the updated place.

BUG=none
TEST=none

Change-Id: I0f94a91afc3d8260723afde62a51de6561c245c7
Reviewed-on: https://chromium-review.googlesource.com/c/1497634
Auto-Submit: Scott Violet <sky@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637143}

cc/README.md

@@ -44,7 +44,7 @@ Design documents for the graphics stack can be found at
 
 ## Other Docs
 
-* [How cc Works](https://docs.google.com/document/d/1yjzOWrPfFGviEd1nru3yzqxSHETC-zsEBSt9C8SvV-Q/edit)
+* [How cc Works](../docs/how_cc_works.md)
 
 ## Glossaries
 

ui/compositor/layer.h

@@ -172,8 +172,8 @@ class COMPOSITOR_EXPORT Layer : public LayerAnimationDelegate,
   // otherwise.
   gfx::Rect GetTargetBounds() const;
 
-  // Sets/gets whether or not drawing of child layers should be clipped to the
-  // bounds of this layer.
+  // Sets/gets whether or not drawing of child layers, including drawing in
+  // this layer, should be clipped to the bounds of this layer.
   void SetMasksToBounds(bool masks_to_bounds);
   bool GetMasksToBounds() const;