cc: Don't discard framebuffer when using partial swaps

cc/output/direct_renderer.h

 // Copyright 2012 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 CC_OUTPUT_DIRECT_RENDERER_H_
 #define CC_OUTPUT_DIRECT_RENDERER_H_
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/containers/scoped_ptr_hash_map.h"
@@ skipping 100 matching lines @@
                       const RenderPass* render_pass,
                       bool allow_partial_swap);
   bool UseRenderPass(DrawingFrame* frame, const RenderPass* render_pass);
 
   virtual void BindFramebufferToOutputSurface(DrawingFrame* frame) = 0;
   virtual bool BindFramebufferToTexture(DrawingFrame* frame,
                                         const ScopedResource* resource,
                                         gfx::Rect target_rect) = 0;
   virtual void SetDrawViewport(gfx::Rect window_space_viewport) = 0;
   virtual void SetScissorTestRect(gfx::Rect scissor_rect) = 0;
-  virtual void ClearFramebuffer(DrawingFrame* frame) = 0;
+  virtual void DiscardPixels(bool has_external_stencil_test,
+                             bool draw_rect_covers_full_surface) = 0;
+  virtual void ClearFramebuffer(DrawingFrame* frame,
+                                bool has_external_stencil_test) = 0;
   virtual void DoDrawQuad(DrawingFrame* frame, const DrawQuad* quad) = 0;
   virtual void BeginDrawingFrame(DrawingFrame* frame) = 0;
   virtual void FinishDrawingFrame(DrawingFrame* frame) = 0;
   virtual void FinishDrawingQuadList();
   virtual bool FlippedFramebuffer() const = 0;
   virtual void EnsureScissorTestEnabled() = 0;
   virtual void EnsureScissorTestDisabled() = 0;
   virtual void DiscardBackbuffer() {}
   virtual void EnsureBackbuffer() {}
 
@@ skipping 16 matching lines @@
 
  private:
   gfx::Vector2d enlarge_pass_texture_amount_;
 
   DISALLOW_COPY_AND_ASSIGN(DirectRenderer);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_DIRECT_RENDERER_H_