Revert of Revert of Per-renderer WebSocket throttling (patchset #1 id:1 of https://codereview.chromium.org/1009303002/)

Reason for revert:
The breakage still persists https://crbug.com/467471 after the original CL was reverted.

Original issue's description:
> Revert of Per-renderer WebSocket throttling (patchset #13 id:300001 of https://codereview.chromium.org/972963002/)
>
> Reason for revert:
> Suspected to have caused WebSocket breakage.
> Failure seen on apprtc.appspot.com and in browser_tests.  Run the manual MANUAL_WorksWithAppRTC test for repro.
>
> See https://code.google.com/p/chromium/issues/detail?id=467471&thanks=467471&ts=1426498439 for details.
>
> Original issue's description:
> > Per-renderer WebSocket throttling
> >
> > Design Doc:
> > https://docs.google.com/document/d/1aw2oN5PKfk-1gLnBrlv1OwLA8K3-ykM2ckwX2lubTg4/edit?usp=sharing
> >
> > BUG=459377
> >
> > Committed: https://crrev.com/58d344316cf2b2cc110619c0fea4979ef143b3a9
> > Cr-Commit-Position: refs/heads/master@{#320074}
>
> TBR=ricea@chromium.org,hiroshige@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=459377
>
> Committed: https://crrev.com/3464a08a0c157c57ea02881687f10058303de8ea
> Cr-Commit-Position: refs/heads/master@{#320705}

TBR=ricea@chromium.org,henrika@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=459377

Review URL: https://codereview.chromium.org/1011743002

Cr-Commit-Position: refs/heads/master@{#320715}

• content/browser/renderer_host/websocket_dispatcher_host.cc[diff]
• content/browser/renderer_host/websocket_dispatcher_host.h[diff]
• content/browser/renderer_host/websocket_dispatcher_host_unittest.cc[diff]
• content/browser/renderer_host/websocket_host.cc[diff]
• content/browser/renderer_host/websocket_host.h[diff]