Remove canTweakAlphaForCoverage from XP's since batch reads flag.

Remove canTweakAlphaForCoverage from XP's since batch reads flag.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/99bc9fdfb555f1cf8e426329633e735e3020b829

[egdaniel, 2015-05-04 19:37:08]

egdaniel@google.com changed reviewers:
+ bsalomon@google.com, joshualitt@chromium.org

[egdaniel, 2015-05-04 19:37:09]

PTAL. Simply removing old, unused code

[joshualitt, 2015-05-04 19:40:13]

On 2015/05/04 19:37:09, egdaniel wrote:
> PTAL. Simply removing old, unused code

lgtm

[egdaniel, 2015-05-04 19:45:11]

The CQ bit was checked by egdaniel@google.com

[commit-bot: I haz the power, 2015-05-04 19:45:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1127693002/1

[commit-bot: I haz the power, 2015-05-04 19:45:38]

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

[commit-bot: I haz the power, 2015-05-04 19:45:39]

Presubmit check for 1127693002-1 failed and returned exit status 1.

Running presubmit commit checks ...

** Presubmit ERRORS **
Since the CL is editing public API, you must have an LGTM from one of:
('reed@chromium.org', 'reed@google.com', 'bsalomon@chromium.org',
'bsalomon@google.com', 'djsollen@chromium.org', 'djsollen@google.com')

[reed1, 2015-05-04 19:54:33]

reed@google.com changed reviewers:
+ reed@google.com

[reed1, 2015-05-04 19:54:33]

api lgtm

[egdaniel, 2015-05-04 19:54:50]

The CQ bit was checked by egdaniel@google.com

[commit-bot: I haz the power, 2015-05-04 19:55:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1127693002/1

[commit-bot: I haz the power, 2015-05-04 19:58:23]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/99bc9fdfb555f1cf8e426329633e735e3020b829