Add a second unsafe ES3 API in command buffer.

gpu/command_buffer/client/gles2_implementation_impl_autogen.h

Index: gpu/command_buffer/client/gles2_implementation_impl_autogen.h
diff --git a/gpu/command_buffer/client/gles2_implementation_impl_autogen.h b/gpu/command_buffer/client/gles2_implementation_impl_autogen.h
index a0d2b5d166f84137dbcc1d07281f908d71abfc53..e6833a319b0e629b3df49dce07bca2b51da3ce83 100644
--- a/gpu/command_buffer/client/gles2_implementation_impl_autogen.h
+++ b/gpu/command_buffer/client/gles2_implementation_impl_autogen.h
@@ -209,6 +209,34 @@ void GLES2Implementation::CompileShader(GLuint shader) {
   CheckGLError();
 }
 
+void GLES2Implementation::CopyBufferSubData(GLenum readtarget,
+                                            GLenum writetarget,
+                                            GLintptr readoffset,
+                                            GLintptr writeoffset,
+                                            GLsizeiptr size) {
+  GPU_CLIENT_SINGLE_THREAD_CHECK();
+  GPU_CLIENT_LOG("[" << GetLogPrefix() << "] glCopyBufferSubData("
+                     << GLES2Util::GetStringBufferTarget(readtarget) << ", "
+                     << GLES2Util::GetStringBufferTarget(writetarget) << ", "
+                     << readoffset << ", " << writeoffset << ", " << size
+                     << ")");
+  if (readoffset < 0) {
+    SetGLError(GL_INVALID_VALUE, "glCopyBufferSubData", "readoffset < 0");
+    return;
+  }
+  if (writeoffset < 0) {
+    SetGLError(GL_INVALID_VALUE, "glCopyBufferSubData", "writeoffset < 0");
+    return;
+  }
+  if (size < 0) {
+    SetGLError(GL_INVALID_VALUE, "glCopyBufferSubData", "size < 0");
+    return;
+  }
+  helper_->CopyBufferSubData(readtarget, writetarget, readoffset, writeoffset,
+                             size);
+  CheckGLError();
+}
+
 void GLES2Implementation::CopyTexImage2D(GLenum target,
                                          GLint level,
                                          GLenum internalformat,