Fix edge-line artifacts issue on Mali

Fix edge-line artifacts issue on Mali

Some GMs show edge-line artifacts on Mali at the bottom/right of the canvas.

Change the 'rtAdjustment' uniform precision from 'midiump' to 'highp' if the GPU vendor is ARM.

NOTE: Vertex Shader should have default 'highp' precision, but now we explicit declared some uniform/attribute precision as 'midiump'.

This patch should fix these issues:

Issue 3693: Some GMs produce random artifacts on Mali in MSAA4
    https://code.google.com/p/skia/issues/detail?id=3693

Issue 3685: srcmode GM has top/right line artifacts on Mali T604 in MSAA4
    https://code.google.com/p/skia/issues/detail?id=3685

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/d18bb23667d11db4779c13253a7e0cd90bf7a57f

[Joel.Liang, 2015-06-02 06:47:59]

joel.liang@arm.com changed reviewers:
+ bsalomon@google.com

[jvanverth1, 2015-06-02 15:57:14]

Just tried this patch with Chrome -- it doesn't appear to address issue 3853.

[jvanverth1, 2015-06-02 15:57:17]

Just tried this patch with Chrome -- it doesn't appear to address issue 3853.

[Joel.Liang, 2015-06-03 07:09:23]

On 2015/06/02 15:57:17, jvanverth1 wrote:
> Just tried this patch with Chrome -- it doesn't appear to address issue 3853.

OK, thanks for your test. I've deleted the statements about 3853 from
description.
And will have a look at 3853 later.

[bsalomon, 2015-06-04 13:46:51]

lgtm

[bsalomon, 2015-06-04 13:46:55]

The CQ bit was checked by bsalomon@google.com

[commit-bot: I haz the power, 2015-06-04 13:47:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1154163012/1

[commit-bot: I haz the power, 2015-06-04 13:52:34]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/d18bb23667d11db4779c13253a7e0cd90bf7a57f