Have Blink be told of scrollbar changes rather than paying attention itself (Blink side).

Source/core/platform/ScrollbarThemeMacCommon.h

Index: Source/core/platform/ScrollbarThemeMacCommon.h
diff --git a/Source/core/platform/ScrollbarThemeMacCommon.h b/Source/core/platform/ScrollbarThemeMacCommon.h
index 8138976c1a393f5d722526c288429099bee8682f..8b5ed94615f9d53735ff945cd782d1887f1426b7 100644
--- a/Source/core/platform/ScrollbarThemeMacCommon.h
+++ b/Source/core/platform/ScrollbarThemeMacCommon.h
@@ -37,7 +37,7 @@ public:
 
     virtual void registerScrollbar(ScrollbarThemeClient*) OVERRIDE;
     virtual void unregisterScrollbar(ScrollbarThemeClient*) OVERRIDE;
-    void preferencesChanged();
+    void preferencesChanged(float, float, bool, bool);

[abarth-chromium, 2013/11/04 00:43:24]

Would you be willing to name these parameters?  It's not clear what they
represent.

[Avi (use Gerrit), 2013/11/04 01:40:24]

Of course I'm willing. I'm writing to fit in with the existing style, but if you
ask for it, you get it.

[abarth-chromium, 2013/11/04 01:41:55]

The existing style is to omit parameter names when they don't add any additional
information.  For example, naming the GraphicsContext* parameters below
|context| wouldn't convey any additional information.

 
     virtual bool supportsControlTints() const OVERRIDE { return true; }