Support for drawing a debug border around animated layers

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index 1969b74967806b7c210a5d0553f2e1da4d1fa7e6..ef55d965dcafe877180e2503362e28df195129b8 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -352,6 +352,11 @@ class CC_EXPORT LayerImpl : LayerAnimationValueObserver {
   float contents_scale_y() const { return draw_properties_.contents_scale_y; }
   void SetContentsScale(float contents_scale_x, float contents_scale_y);
 
+  // Computes a box in screen space that should entirely contain the layer's
+  // bounds through the entirety of the layer's current animation. Returns true
+  // on success.

[Ian Vollick, 2013/11/28 00:44:58]

It's not quite success, IIRC. I thought we returned false if the layer was
unaffected by an animation? It returns true whenever we need to inflate bounds
to account for animation, right?

[Ian Vollick, 2013/12/06 20:24:28]

Alex pointed out offline, that although we'll return false when we're not
animated, |box| in that case really won't be correct (I thought it would
previously). The problem is that for |box| to be correct, it would still have to
be transformed into screen space by all the static transforms in the hierarchy,
but we skip this work.

tl;dr - Ignore me :)

[avallee, 2013/12/06 22:08:32]

Tweaked the comment.

+  bool GetAnimationBounds(gfx::BoxF* out) const { return false; }
+
   virtual void CalculateContentsScale(float ideal_contents_scale,
                                       float device_scale_factor,
                                       float page_scale_factor,