Revert of Increase YUV video clamping

Revert of Increase YUV video clamping (patchset #4 id:60001 of https://codereview.chromium.org/1008493002/)

Reason for revert:
I think this patch caused blink layouttest failures (e.g., media/video-colorspace-yuv420.html). See http://crbug.com/467283

Original issue's description:
> Increase YUV video clamping
>
> The current clamping is not enough to avoid bleeding issues. This is
> exposed when changing the background color in CreateEdgeBleedPass from
> black to gray. The reason it works now is because interpolating U/V
> textures from black (YUV = 0, 0, 0) to green (YUV = 149, 43, 21) will
> still result in saturated green pixels (RGB = 0, 255, 0). All YUV values
> in the range (149, 0-43, 0-21) will end up as RGB = (0, 255, 0).
>
> The current clamping is not enough, because the calculation
> '0.5f / quad->tex_size.width()' is using the Y texture size, the highest
> resolution plane, but the U/V texture size is only half of that. This CL
> changes tex_size to represent the lowest resolution texture instead.
>
> BUG=429640
>
> Committed: https://crrev.com/4be817dd606efdba1614d32608ddd6e16bfa687d
> Cr-Commit-Position: refs/heads/master@{#320567}

TBR=enne@chromium.org,danakj@chromium.org,wfh@chromium.org,magjed@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=429640, 467283
Committed: https://crrev.com/9764be34e6e97a05a0bff5a4448a5ac56e735b85
Cr-Commit-Position: refs/heads/master@{#320642}

[pdr., 2015-03-14 04:24:39]

Created Revert of Increase YUV video clamping

[pdr., 2015-03-14 04:24:59]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2015-03-14 04:25:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1007953003/1

[commit-bot: I haz the power, 2015-03-14 04:25:53]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-14 04:26:31]

Patchset 1 (id:??) landed as
https://crrev.com/9764be34e6e97a05a0bff5a4448a5ac56e735b85
Cr-Commit-Position: refs/heads/master@{#320642}