Revert of Removed arbitrary 4096 size limit on WebGL canvas backbuffers

Revert of Removed arbitrary 4096 size limit on WebGL canvas backbuffers (patchset #1 id:1 of https://codereview.chromium.org/1002523007/)

Reason for revert:
Suspected to break GPU bots, in the regression range of http://build.chromium.org/p/chromium.gpu/builders/Win7%20Release%20%28NVIDIA%29/builds/30393 which fails with WebglConformance.conformance_canvas_drawingbuffer_static_canvas_test. Another bot has the following error for that test so it could be related
[1263:1287:0319/210147:INFO:CONSOLE(11)] "gl.drawingBufferWidth == 50 should be true. Was false.", source:  (11)
http://build.chromium.org/p/chromium.webkit/builders/GPU%20Mac%2010.9%20%28Intel%29/builds/9300/steps/webgl_conformance_tests/logs/WebglConformance.conformance_canvas_drawingbuffer_static_canvas_test

Original issue's description:
> Removed arbitrary 4096 size limit on WebGL canvas backbuffers
> 
> BUG=445542
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=192222

TBR=kbr@chromium.org,zmo@chromium.org,bajones@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=445542
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=192259

[Corentin Wallez, 2015-03-20 14:58:17]

Created Revert of Removed arbitrary 4096 size limit on WebGL canvas backbuffers

[commit-bot: I haz the power, 2015-03-20 14:58:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1022113002/1

[commit-bot: I haz the power, 2015-03-20 14:58:42]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-03-20 14:58:43]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[bajones, 2015-03-20 15:48:02]

lgtm

[bajones, 2015-03-20 15:48:04]

The CQ bit was checked by bajones@chromium.org

[commit-bot: I haz the power, 2015-03-20 15:48:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1022113002/1

[commit-bot: I haz the power, 2015-03-20 15:49:04]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=192259