Introduce the MicButtonTargeter class

ui/views/masked_view_targeter.h

Index: ui/views/masked_view_targeter.h
diff --git a/ui/views/masked_view_targeter.h b/ui/views/masked_view_targeter.h
index 9a70c9e5b6a057814d61e6d4a9bde217583663ed..0b324371f76a810fc299e0e3994f66b6ad84f4d6 100644
--- a/ui/views/masked_view_targeter.h
+++ b/ui/views/masked_view_targeter.h
@@ -23,11 +23,11 @@ class VIEWS_EXPORT MaskedViewTargeter : public ViewTargeter {
   explicit MaskedViewTargeter(View* masked_view);
   virtual ~MaskedViewTargeter();
 
- protected:
   // Sets the hit-test mask for |view| in |mask| (in |view|'s local
   // coordinate system). Returns whether a valid mask has been set in |mask|.
-  virtual bool GetHitTestMask(View* view, gfx::Path* mask) const = 0;
+  virtual bool GetHitTestMask(const View* view, gfx::Path* mask) const = 0;
 
+ protected:
   // ui::EventTargeter:
   virtual bool EventLocationInsideBounds(
       ui::EventTarget* target,