ui: Cache the output of View::OnPaint when the View isn't invalid.

ui/compositor/paint_recorder.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_COMPOSITOR_PAINT_RECORDER_H_
 #define UI_COMPOSITOR_PAINT_RECORDER_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "skia/ext/refptr.h"
 #include "ui/compositor/compositor_export.h"
 
 namespace cc {
 class DisplayItemList;
 }
 
 namespace gfx {
 class Canvas;
 }
 
 class SkCanvas;
 class SkPictureRecorder;
 
 namespace ui {
+class PaintCache;
 class PaintContext;
 
 // A class to hide the complexity behind setting up a recording into a
 // DisplayItem. This is meant to be short-lived within the scope of recording
 // taking place, the DisplayItem should be removed from the PaintRecorder once
 // recording is complete and can be cached.
 class COMPOSITOR_EXPORT PaintRecorder {
  public:
+  PaintRecorder(const PaintContext& context, PaintCache* cache);

[sky, 2015/04/23 16:29:00]

Document ownership/lifetime of PaintCache.

[danakj, 2015/04/23 16:34:09]

OK. To me raw pointer implies weak pointer that you don't own, but I'll add a
comment saying so.

   explicit PaintRecorder(const PaintContext& context);
   ~PaintRecorder();
 
   // Gets a gfx::Canvas for painting into.
   gfx::Canvas* canvas() { return canvas_; }
 
  private:
   const PaintContext& context_;
   gfx::Canvas* canvas_;
   scoped_ptr<gfx::Canvas> owned_canvas_;
+  PaintCache* cache_;
 
   DISALLOW_COPY_AND_ASSIGN(PaintRecorder);
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_PAINT_RECORDER_H_