Fix various issues with framebuffer fetch

Fix various issues with framebuffer fetch

This CL does two things. First it fixes a bug of ours where when using
a custom fbFetch variable (es 3.0 and higher), we sometimes overwrite
the out color and then attempt to use it as the dst color later. This is
fixed here by using an intermediate variable.

Secondly I've added a workaround to an andreno fbFetch where reading from
the outColor always returns the original dstColor even if we've overwritten
the value.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2248403003

Committed: https://skia.googlesource.com/skia/+/138c26300f2686175f68b5a3528133f5c9edb596

[egdaniel, 2016-08-17 17:02:59]

Description was changed from

==========
Fix various issues with framebuffer fetch

This CL does two things. First it fixes a bug of ours where when using
a custom fbFetch variable (es 3.0 and higher), we sometimes overwrite
the out color and then attempt to use it as the dst color later. This is
fixed here by using an intermediate variable.

Secondly I've added a workaround to an andreno fbFetch where reading from
the outColor always returns the original dstColor even if we've overwritten
the value.

BUG=skia:
==========

to

==========
Fix various issues with framebuffer fetch

This CL does two things. First it fixes a bug of ours where when using
a custom fbFetch variable (es 3.0 and higher), we sometimes overwrite
the out color and then attempt to use it as the dst color later. This is
fixed here by using an intermediate variable.

Secondly I've added a workaround to an andreno fbFetch where reading from
the outColor always returns the original dstColor even if we've overwritten
the value.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2248403003
==========

[egdaniel, 2016-08-17 17:07:30]

egdaniel@google.com changed reviewers:
+ brianosman@google.com, bsalomon@google.com

[bsalomon, 2016-08-17 17:28:42]

lgtm

[egdaniel, 2016-08-17 17:32:41]

The CQ bit was checked by egdaniel@google.com

[commit-bot: I haz the power, 2016-08-17 17:32:47]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-17 17:59:02]

Description was changed from

==========
Fix various issues with framebuffer fetch

This CL does two things. First it fixes a bug of ours where when using
a custom fbFetch variable (es 3.0 and higher), we sometimes overwrite
the out color and then attempt to use it as the dst color later. This is
fixed here by using an intermediate variable.

Secondly I've added a workaround to an andreno fbFetch where reading from
the outColor always returns the original dstColor even if we've overwritten
the value.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2248403003
==========

to

==========
Fix various issues with framebuffer fetch

This CL does two things. First it fixes a bug of ours where when using
a custom fbFetch variable (es 3.0 and higher), we sometimes overwrite
the out color and then attempt to use it as the dst color later. This is
fixed here by using an intermediate variable.

Secondly I've added a workaround to an andreno fbFetch where reading from
the outColor always returns the original dstColor even if we've overwritten
the value.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2248403003

Committed:
https://skia.googlesource.com/skia/+/138c26300f2686175f68b5a3528133f5c9edb596
==========

[commit-bot: I haz the power, 2016-08-17 17:59:03]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/138c26300f2686175f68b5a3528133f5c9edb596