Revert of Flush pending writes on Skia scratch textures used in Chromium (patchset...

Revert of Flush pending writes on Skia scratch textures used in Chromium (patchset #4 id:60001 of https://codereview.chromium.org/1225583003/)

Reason for revert:
Broke three video-related WebGL conformance tests on Nexus 5; see https://code.google.com/p/chromium/issues/detail?id=504773#c3 .

Original issue's description:
> Flush pending writes on Skia scratch textures used in Chromium
>
> Chromium uses textures allocated by Skia's internal resource manager for
> video rendering. In case the textures are recycled, they might have
> pending write operations on them. Most commonly they have a pending
> framebuffer discard that gets inserted when a texture is chosen for
> recycling. These pending operations need to be flushed before the texture
> is accessed outside of Skia. Otherwise it's possible that the pending
> operations get deferred until after Chromium uses the texture.
>
> In other words, we need to guarantee that the order of operations is:
>
> 1. Pending writes from Skia are flushed
> 2. Chromium writes to the texture without involving Skia
> 3. Chromium requests a readback of the texture using Skia
> 4. Skia reads back the texture
>
> instead of
>
> 1. Chromium writes to the texture without involving Skia
> 2. Chromium requests a readback of the texture using Skia
> 3. Pending writes from Skia are flushed
> 4. Skia reads back the texture
>
> BUG=504773, 499555
> TEST=WebGL conformance tests
>
> Committed: https://crrev.com/140faf7e1dbc0f41a57242b4d3114bad6b9552fd
> Cr-Commit-Position: refs/heads/master@{#338089}

TBR=dalecurtis@chromium.org,qinmin@chromium.org,bsalomon@google.com,xhwang@chromium.org,oetuaho@nvidia.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=504773, 499555

Review URL: https://codereview.chromium.org/1226093008

Cr-Commit-Position: refs/heads/master@{#338165}