Fix context sharing between channels to be order-independent.

Fix context sharing between channels to be order-independent.

Ensuring order of channel recreation after a GPU process death is very hard.
With this there's not need. A channel is either shared or not, all the "shared"
channels share their context together, every other one doesn't share with
anything. More restrictive but it's enough for our needs.

BUG=116913
TEST=chrome --ui-use-gpu-process, kill GPU process, observe GpuChannelManager::OnEstablishChannel crash doesn't happen.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=125521

[piman, 2012-03-07 19:50:24]

apatrick: please review
ben: OWNERS

[apatrick_chromium, 2012-03-07 20:58:08]

lgtm

[Ben Goodger (Google), 2012-03-08 00:48:37]

lgtm