cc: Use maximum tiling contents scales for picture layer scale

cc/layer_impl.h

Index: cc/layer_impl.h
diff --git a/cc/layer_impl.h b/cc/layer_impl.h
index 4b98f762668e94371f949c02e1b3e1d6d2b8b5e6..35dbd939845e1308622ab4a1ee7c88c6954bfde7 100644
--- a/cc/layer_impl.h
+++ b/cc/layer_impl.h
@@ -198,6 +198,12 @@ public:
     float contentsScaleY() const { return m_drawProperties.contents_scale_y; }
     void setContentsScale(float contentsScaleX, float contentsScaleY);
 
+    virtual void calculateContentsScale(

[danakj, 2013/01/07 15:57:44]

So, this never actually sets the return values on the impl side right? The
float* and gfx::Size* will always be untouched in the current versions of this
method.

Should we add a comment saying that the draw properties are already set on impl
by push properties, and this is just to inform the layers about the ideal
contents scale?

Is it worth having these pointers here that could let a layer override the
contents scale/bounds on impl and not match the main thread (and also not match
any data from the main thread)?

What's your thinking long-term here?

[enne (OOO), 2013/01/07 17:00:01]

The whole point of this function is so that a (Picture)LayerImpl can override
the values from the main thread.  This is my long-term thinking at the moment.

You are correct that most layers get their values from push properties and don't
have any need or ability to change their content bounds or content scale.

PTAL at the newest version.  I added a comment and set the out parameters to the
draw properties themselves to make it clearer.

+        float idealContentsScale,
+        float* contentsScaleX,
+        float* contentsScaleY,
+        gfx::Size* contentBounds) { }
+
     gfx::Vector2d scrollOffset() const { return m_scrollOffset; }
     void setScrollOffset(gfx::Vector2d);