Proposal for GWT patch review policy

[Bhaskar]

As per last SC meeting, I took the action item to come up with a doc that talks to how we want to manage contributions to GWT. Here's link to the draft version:

https://docs.google.com/document/d/1_dBGeyqwMaLVXZ48VkOWz64bdLBdUeQgsvY8PEcXyMU/edit?usp=sharing

Please add comments to the doc. 

Thanks,

Bhaskar