Add shader link validation test for variant/invariant varying mismatch.
Clean up some of the setTimeout() in the tests.

Some should be replaced with waitForComposite,
some should be replaced with requestAnimFrame,
some should use the timeout 0 instead of a positive value.
Add comments pointing to the spec.
Merge pull request #730 from zhenyao/varying

Add shader link validation test for variant/invariant varying mismatch.
Use wtu.checkCanvasRect when we can.
Merge pull request #731 from zhenyao/timeout

Clean up some of the setTimeout() in the tests.
Merge pull request #732 from zhenyao/clean

Use wtu.checkCanvasRect when we can.
Fixed dates on new tests and removed unused codepaths
Merge pull request #733 from toji/date_fixup

Fixed dates on new tests and removed unused codepaths
Move invariant related tests into a new file and add more cases.
Fix year in disclaimer.
Add texStorage2D test
Add more cases
Merge pull request #734 from zhenyao/invariant

Invariant
Merge pull request #735 from bjacob/texstorage2d

Add texStorage2D test
add WebGL2 conformance test for new texture formats, and sized internalformats
Merge pull request #736 from bjacob/tex-new-formats

WebGL2 test for new formats and sized internalformats
Add tests for texture copying feedback loops behavior.
Updated the EXT_sRGB conformance test to test more code paths.
Merge pull request #737 from zhenyao/loop

Add tests for texture copying feedback loops behavior.