Make View::Paint use ui::PaintRecorder to access PaintContext's canvas

ui/compositor/paint_context.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_CONTEXT_H_
 #define UI_COMPOSITOR_PAINT_CONTEXT_H_
 
 #include "base/logging.h"
 #include "ui/compositor/compositor_export.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace gfx {
 class Canvas;
 }
 
 namespace ui {
+class PaintRecorder;
 
 class COMPOSITOR_EXPORT PaintContext {
  public:
   // Construct a PaintContext that can only re-paint the area in the
   // |invalidation|.
   PaintContext(gfx::Canvas* canvas, const gfx::Rect& invalidation)
       : canvas_(canvas), invalidation_(invalidation) {
 #if DCHECK_IS_ON()
     root_visited_ = nullptr;
 #endif
@@ skipping 34 matching lines @@
 #if DCHECK_IS_ON()
   void Visited(void* visited) const {
     if (!root_visited_)
       root_visited_ = visited;
   }
   void* RootVisited() const { return root_visited_; }
   const gfx::Vector2d& PaintOffset() const { return offset_; }
 #endif
 
  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
+  // recorder to access them.
+  friend class PaintRecorder;
+
   // Clone a PaintContext with an additional |offset|.
   PaintContext(const PaintContext& other, const gfx::Vector2d& offset)
       : canvas_(other.canvas_),
         invalidation_(other.invalidation_),
         offset_(other.offset_ + offset) {
 #if DCHECK_IS_ON()
     root_visited_ = other.root_visited_;
 #endif
   }
 
   gfx::Canvas* canvas_;
   // Invalidation in the space of the paint root (ie the space of the layer
   // backing the paint taking place).
   gfx::Rect invalidation_;
   // Offset from the PaintContext to the space of the paint root and the
   // |invalidation_|.
   gfx::Vector2d offset_;
 
 #if DCHECK_IS_ON()
   // Used to verify that the |invalidation_| is only used to compare against
   // rects in the same space.
   mutable void* root_visited_;
 #endif
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_PAINT_CONTEXT_H_