Fix WebGLDebugShaders::getTranslatedShaderSource returning null

Fix WebGLDebugShaders::getTranslatedShaderSource returning null

The function should return an empty string in case no source has been
defined, compileShader() has not been called, or the translation has
failed for shader. It used to return null, after this patch it returns an
empty string like it is supposed to.

Also make getTranslatedShaderSourceANGLE pure virtual in
WebGraphicsContext3D.

BUG=358530
TEST=WebGL conformance tests with --enable-privileged-webgl-extensions
R=kbr@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170645

[oetuaho-nv, 2014-04-01 09:11:40]

Messaged chrome-troopers about the bot failures, they look unrelated.

[Ken Russell (switch to Gerrit), 2014-04-01 22:50:52]

Thanks for the fix. LGTM

[oetuaho-nv, 2014-04-02 07:34:58]

The CQ bit was checked by oetuaho@nvidia.com

[commit-bot: I haz the power, 2014-04-02 07:35:09]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/oetuaho@nvidia.com/216603004/1

[commit-bot: I haz the power, 2014-04-02 07:47:21]

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

[commit-bot: I haz the power, 2014-04-02 07:47:21]

Try jobs failed on following builders:
  tryserver.blink on blink_presubmit

[oetuaho-nv, 2014-04-02 08:01:09]

Adding some folks from public/OWNERS, please review.

[jochen (gone - plz use gerrit), 2014-04-02 09:22:36]

lgtm

[oetuaho-nv, 2014-04-02 09:59:17]

The CQ bit was checked by oetuaho@nvidia.com

[commit-bot: I haz the power, 2014-04-02 09:59:24]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/oetuaho@nvidia.com/216603004/1

[commit-bot: I haz the power, 2014-04-02 10:08:17]

Change committed as 170645