Add a second unsafe ES3 API in command buffer.

gpu/command_buffer/client/gles2_cmd_helper_autogen.h

Index: gpu/command_buffer/client/gles2_cmd_helper_autogen.h
diff --git a/gpu/command_buffer/client/gles2_cmd_helper_autogen.h b/gpu/command_buffer/client/gles2_cmd_helper_autogen.h
index a4cbe22f70844b44c38e723538a1522ae950e9c7..1556c26c155685e25d9cc92f9ee2cffd81f3d60e 100644
--- a/gpu/command_buffer/client/gles2_cmd_helper_autogen.h
+++ b/gpu/command_buffer/client/gles2_cmd_helper_autogen.h
@@ -243,6 +243,18 @@ void CompressedTexSubImage2D(GLenum target,
   }
 }
 
+void CopyBufferSubData(GLenum readtarget,
+                       GLenum writetarget,
+                       GLintptr readoffset,
+                       GLintptr writeoffset,
+                       GLsizeiptr size) {
+  gles2::cmds::CopyBufferSubData* c =
+      GetCmdSpace<gles2::cmds::CopyBufferSubData>();
+  if (c) {
+    c->Init(readtarget, writetarget, readoffset, writeoffset, size);
+  }
+}
+
 void CopyTexImage2D(GLenum target,
                     GLint level,
                     GLenum internalformat,