Fixes a bug when the framebuffer is cleared with invalid scissor rect

cc/gl_renderer.h

 // Copyright 2010 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_GL_RENDERER_H_
 #define CC_GL_RENDERER_H_
 
 #include "cc/cc_export.h"
 #include "cc/checkerboard_draw_quad.h"
 #include "cc/debug_border_draw_quad.h"
@@ skipping 69 matching lines @@
     virtual void setScissorTestRect(const gfx::Rect& scissorRect) OVERRIDE;
     virtual void clearFramebuffer(DrawingFrame&) OVERRIDE;
     virtual void drawQuad(DrawingFrame&, const DrawQuad*) OVERRIDE;
     virtual void beginDrawingFrame(DrawingFrame&) OVERRIDE;
     virtual void finishDrawingFrame(DrawingFrame&) OVERRIDE;
     virtual bool flippedFramebuffer() const OVERRIDE;
     virtual void ensureScissorTestEnabled() OVERRIDE;
     virtual void ensureScissorTestDisabled() OVERRIDE;
     virtual void finishDrawingQuadList() OVERRIDE;
 
+public:
+    void enableScissorForTesting() { ensureScissorTestEnabled(); }
+
 private:
     static void toGLMatrix(float*, const gfx::Transform&);
     static ManagedMemoryPolicy::PriorityCutoff priorityCutoff(WebKit::WebGraphicsMemoryAllocation::PriorityCutoff);
 
     void drawCheckerboardQuad(const DrawingFrame&, const CheckerboardDrawQuad*);
     void drawDebugBorderQuad(const DrawingFrame&, const DebugBorderDrawQuad*);
     scoped_ptr<ScopedResource> drawBackgroundFilters(
         DrawingFrame&, const RenderPassDrawQuad*,
         const gfx::Transform& contentsDeviceTransform,
         const gfx::Transform& contentsDeviceTransformInverse);
@@ skipping 143 matching lines @@
 #if DEBUG_GL_CALLS && !defined(NDEBUG)
 #define GLC(context, x) (x, GLRenderer::debugGLCall(&*context, #x, __FILE__, __LINE__))
 #else
 #define GLC(context, x) (x)
 #endif
 
 
 }
 
 #endif  // CC_GL_RENDERER_H_