cc: Don't discard framebuffer when using partial swaps

cc/output/software_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_SOFTWARE_RENDERER_H_
 #define CC_OUTPUT_SOFTWARE_RENDERER_H_
 
 #include "base/basictypes.h"
 #include "cc/base/cc_export.h"
 #include "cc/output/compositor_frame.h"
@@ skipping 39 matching lines @@
   virtual void EnsureBackbuffer() OVERRIDE;
 
  protected:
   virtual void BindFramebufferToOutputSurface(DrawingFrame* frame) OVERRIDE;
   virtual bool BindFramebufferToTexture(
       DrawingFrame* frame,
       const ScopedResource* texture,
       gfx::Rect target_rect) OVERRIDE;
   virtual void SetDrawViewport(gfx::Rect window_space_viewport) OVERRIDE;
   virtual void SetScissorTestRect(gfx::Rect scissor_rect) OVERRIDE;
-  virtual void ClearFramebuffer(DrawingFrame* frame) OVERRIDE;
+  virtual void DiscardPixels(bool has_external_stencil_test,
+                             bool draw_rect_covers_full_surface) OVERRIDE;
+  virtual void ClearFramebuffer(DrawingFrame* frame,
+                                bool has_external_stencil_test) OVERRIDE;
   virtual void DoDrawQuad(DrawingFrame* frame, const DrawQuad* quad) OVERRIDE;
   virtual void BeginDrawingFrame(DrawingFrame* frame) OVERRIDE;
   virtual void FinishDrawingFrame(DrawingFrame* frame) OVERRIDE;
   virtual bool FlippedFramebuffer() const OVERRIDE;
   virtual void EnsureScissorTestEnabled() OVERRIDE;
   virtual void EnsureScissorTestDisabled() OVERRIDE;
   virtual void CopyCurrentRenderPassToBitmap(
       DrawingFrame* frame,
       scoped_ptr<CopyOutputRequest> request) OVERRIDE;
 
@@ skipping 37 matching lines @@
   scoped_ptr<ResourceProvider::ScopedWriteLockSoftware>
       current_framebuffer_lock_;
   scoped_ptr<SoftwareFrameData> current_frame_data_;
 
   DISALLOW_COPY_AND_ASSIGN(SoftwareRenderer);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_SOFTWARE_RENDERER_H_