Remove some dead code in ThumbnailGenerator.

Remove some dead code in ThumbnailGenerator.

The aim of this change is to remove the use of RenderWidgetHost::CopyFromBackingStore.
|prefer_backing_store| in AskForSnapShot is always set to false, so I deleted the pass that executes only when true is set in order to remove GetBitmapForRenderWidgetHost, which eventually calls RenderWidgetHost::CopyFromBackingStore.

BUG=120003
TEST=Checked tab overview works file
Tests-Missing

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=135788

[mazda, 2012-05-05 04:58:31]

Could you review this change?

brettw: Overall change
avi: chrome/browser/ui/cocoa

Thanks,

[brettw, 2012-05-07 22:23:32]

lgtm

[Avi (use Gerrit), 2012-05-07 22:38:25]

LGTM

On Mon, May 7, 2012 at 6:23 PM, <brettw@chromium.org> wrote:

> lgtm
>
>
>
>
http://codereview.chromium.**org/10348007/<http://codereview.chromium.org/103...
>

[commit-bot: I haz the power, 2012-05-07 22:40:08]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mazda@chromium.org/10348007/17001

[commit-bot: I haz the power, 2012-05-08 01:17:59]

Try job failure for 10348007-17001 (retry) on win_rel for step "update".
It's a second try, previously, step "browser_tests" failed.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

Step "update" is always a major failure.
Look at the try server FAQ for more details.

[commit-bot: I haz the power, 2012-05-08 01:22:26]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mazda@chromium.org/10348007/17001

[commit-bot: I haz the power, 2012-05-08 01:46:00]

Try job failure for 10348007-17001 on win_rel for step "update".
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

Step "update" is always a major failure.
Look at the try server FAQ for more details.