Implement EXT_draw_buffers WebGL extention support in command buffer.

gpu/command_buffer/common/gles2_cmd_format_test_autogen.h

Index: gpu/command_buffer/common/gles2_cmd_format_test_autogen.h
===================================================================
--- gpu/command_buffer/common/gles2_cmd_format_test_autogen.h	(revision 187725)
+++ gpu/command_buffer/common/gles2_cmd_format_test_autogen.h	(working copy)
@@ -4457,5 +4457,46 @@
       next_cmd, sizeof(cmd));
 }
 
+TEST_F(GLES2FormatTest, DrawBuffersEXT) {
+  cmds::DrawBuffersEXT& cmd = *GetBufferAs<cmds::DrawBuffersEXT>();
+  void* next_cmd = cmd.Set(
+      &cmd,
+      static_cast<GLsizei>(11),
+      static_cast<uint32>(12),
+      static_cast<uint32>(13));
+  EXPECT_EQ(static_cast<uint32>(cmds::DrawBuffersEXT::kCmdId),
+            cmd.header.command);
+  EXPECT_EQ(sizeof(cmd), cmd.header.size * 4u);
+  EXPECT_EQ(static_cast<GLsizei>(11), cmd.count);
+  EXPECT_EQ(static_cast<uint32>(12), cmd.bufs_shm_id);
+  EXPECT_EQ(static_cast<uint32>(13), cmd.bufs_shm_offset);
+  CheckBytesWrittenMatchesExpectedSize(
+      next_cmd, sizeof(cmd));
+}
+
+TEST_F(GLES2FormatTest, DrawBuffersEXTImmediate) {
+  const int kSomeBaseValueToTestWith = 51;
+  static GLenum data[] = {
+    static_cast<GLenum>(kSomeBaseValueToTestWith + 0),
+  };
+  cmds::DrawBuffersEXTImmediate& cmd =
+      *GetBufferAs<cmds::DrawBuffersEXTImmediate>();
+  const GLsizei kNumElements = 1;
+  const size_t kExpectedCmdSize =
+      sizeof(cmd) + kNumElements * sizeof(GLenum) * 1;
+  void* next_cmd = cmd.Set(
+      &cmd,
+      static_cast<GLsizei>(1),
+      data);
+  EXPECT_EQ(static_cast<uint32>(cmds::DrawBuffersEXTImmediate::kCmdId),
+            cmd.header.command);
+  EXPECT_EQ(kExpectedCmdSize, cmd.header.size * 4u);
+  EXPECT_EQ(static_cast<GLsizei>(1), cmd.count);
+  CheckBytesWrittenMatchesExpectedSize(
+      next_cmd, sizeof(cmd) +
+      RoundSizeToMultipleOfEntries(sizeof(data)));
+  // TODO(gman): Check that data was inserted;
+}
+
 #endif  // GPU_COMMAND_BUFFER_COMMON_GLES2_CMD_FORMAT_TEST_AUTOGEN_H_