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..05730593dad1d37f7f138bfcb0df3ebda77f9a70 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(
+        float idealContentsScale,
+        float* contentsScaleX,
+        float* contentsScaleY,
+        gfx::Size* contentBounds);
+
     gfx::Vector2d scrollOffset() const { return m_scrollOffset; }
     void setScrollOffset(gfx::Vector2d);