Add gl tests to make sure when a buffer is unmapped, all access path generates an INVALID_OPERATION.

gpu/command_buffer/service/transform_feedback_manager.cc

Index: gpu/command_buffer/service/transform_feedback_manager.cc
diff --git a/gpu/command_buffer/service/transform_feedback_manager.cc b/gpu/command_buffer/service/transform_feedback_manager.cc
index e474c0bc07baf69eb65dac5056ac713f9ecbeee8..0c04fcd7749873aae4e7a90139175ccf1dc84829 100644
--- a/gpu/command_buffer/service/transform_feedback_manager.cc
+++ b/gpu/command_buffer/service/transform_feedback_manager.cc
@@ -114,12 +114,5 @@ void TransformFeedbackManager::RemoveTransformFeedback(GLuint client_id) {
   }
 }
 
-void TransformFeedbackManager::RemoveBoundBuffer(Buffer* buffer) {
-  for (auto iter = transform_feedbacks_.begin();
-       iter != transform_feedbacks_.end(); ++iter) {
-    iter->second->RemoveBoundBuffer(buffer);
-  }
-}
-
 }  // namespace gles2
 }  // namespace gpu