Bug 1048747 - [WebGL2] Implement uniform block/buffer. r=jgilbert, r=smaug

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extra : rebase_source : cdd24494397c9b6ce9f7103c78b8432107ddc20f
extra : source : dadf008b2b7a14d0c308ab4c8eae6001fb5f7492
extra : histedit_source : 90b49de9e294dd8e89a666fa9b3025892a6cf4e6