ui: Make compositor unittests access the canvas through PaintRecorder.

ui/compositor/paint_context.h

Index: ui/compositor/paint_context.h
diff --git a/ui/compositor/paint_context.h b/ui/compositor/paint_context.h
index 0960ab5478f6336e32925cf1659f396c9e007de9..914f9a9f04ca3ac3393b6cc280af8c0510827173 100644
--- a/ui/compositor/paint_context.h
+++ b/ui/compositor/paint_context.h
@@ -67,6 +67,8 @@ class PaintContext {
   const gfx::Vector2d& PaintOffset() const { return offset_; }
 #endif
 
+  const gfx::Rect& InvalidationForTesting() const { return invalidation_; }

[sadrul, 2015/04/07 19:05:12]

In a number of components, we expose such things through a TestApi (grep for
TestApi in //ui/) instead of *ForTesting() methods to avoid misuse/accidental
use of test-apis in real code.

[danakj, 2015/04/07 20:09:35]

FWIW Presubmit makes an error if you use a method named ForTesting in a non-test
file.

I wanted to subclass but then I'd have to inject a testing PaintContext into
ui::Layer. I guess a friend class would work too, hm. That's slightly nicer as
it keeps more code/api out of prod. But it also moves access to private things
somewhere else, hm hm.

I think I'll go with it as this for now.. but I wanna think about this TestAPI
idea, thanks for pointing it out.

+
  private:
   // The PaintRecorder needs access to the internal canvas and friends, but we
   // don't want to expose them on this class so that people must go through the