Ensure alpha channel in backbuffer is correct with DirectComposition.

gpu/command_buffer/service/gles2_cmd_decoder_unittest_framebuffers.cc

 // Copyright 2014 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.
 
 #include "gpu/command_buffer/service/gles2_cmd_decoder.h"
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 2749 matching lines @@
 
   // EXPECT_EQ can't be used to compare function pointers
   EXPECT_TRUE(
       gfx::MockGLInterface::GetGLProcAddress("glInvalidateFramebuffer") !=
       gfx::g_driver_gl.fn.glDiscardFramebufferEXTFn);
   EXPECT_TRUE(
       gfx::MockGLInterface::GetGLProcAddress("glInvalidateFramebuffer") !=
       gfx::MockGLInterface::GetGLProcAddress("glDiscardFramebufferEXT"));
 }
 
+TEST_P(GLES2DecoderManualInitTest, ClearBackbufferBitsOnFlipSwap) {
+  InitState init;
+  init.gl_version = "opengl es 2.0";
+  InitDecoder(init);
+  surface_->set_buffers_flipped(true);
+
+  EXPECT_EQ(0u, GetAndClearBackbufferClearBitsForTest());
+
+  SwapBuffers& cmd = *GetImmediateAs<SwapBuffers>();
+  cmd.Init();
+  EXPECT_EQ(error::kNoError, ExecuteCmd(cmd));
+  EXPECT_EQ(GL_NO_ERROR, GetGLError());
+  EXPECT_EQ(static_cast<uint32_t>(GL_COLOR_BUFFER_BIT),
+            GetAndClearBackbufferClearBitsForTest());
+
+  EXPECT_EQ(error::kNoError, ExecuteCmd(cmd));
+  EXPECT_EQ(GL_NO_ERROR, GetGLError());
+  EXPECT_EQ(0u, GetAndClearBackbufferClearBitsForTest());
+
+  ResizeCHROMIUM& resize_cmd = *GetImmediateAs<ResizeCHROMIUM>();
+  resize_cmd.Init(1, 1, 1.0f, GL_TRUE);
+  EXPECT_EQ(error::kNoError, ExecuteCmd(resize_cmd));
+  EXPECT_EQ(GL_NO_ERROR, GetGLError());
+  EXPECT_EQ(static_cast<uint32_t>(GL_COLOR_BUFFER_BIT),
+            GetAndClearBackbufferClearBitsForTest());
+
+  cmd.Init();
+  EXPECT_EQ(error::kNoError, ExecuteCmd(cmd));
+  EXPECT_EQ(GL_NO_ERROR, GetGLError());
+  EXPECT_EQ(static_cast<uint32_t>(GL_COLOR_BUFFER_BIT),
+            GetAndClearBackbufferClearBitsForTest());
+
+  EXPECT_EQ(error::kNoError, ExecuteCmd(cmd));
+  EXPECT_EQ(GL_NO_ERROR, GetGLError());
+  EXPECT_EQ(0u, GetAndClearBackbufferClearBitsForTest());
+}
+
 TEST_P(GLES2DecoderManualInitTest, DiscardFramebufferEXT) {
   InitState init;
   init.extensions = "GL_EXT_discard_framebuffer";
   init.gl_version = "opengl es 2.0";
   InitDecoder(init);
 
   // EXPECT_EQ can't be used to compare function pointers
   EXPECT_TRUE(
       gfx::MockGLInterface::GetGLProcAddress("glDiscardFramebufferEXT") ==
       gfx::g_driver_gl.fn.glDiscardFramebufferEXTFn);
@@ skipping 310 matching lines @@
   EXPECT_EQ(1, result->GetNumResults());
   EXPECT_EQ(GL_NO_ERROR, GetGLError());
 }
 
 // TODO(gman): PixelStorei
 
 // TODO(gman): SwapBuffers
 
 }  // namespace gles2
 }  // namespace gpu