[Test] Disable WebGLInfoBarTest.

Disabling following flaky tests on Mac:
WebGLInfoBarTest.ContextLossRaisesInfoBar
WebGLInfoBarTest.ContextLossInfoBarReload

TBR=zmo@chromium.org, danakj@chromium.org
BUG=324555
NOTRY=true

Review URL: https://codereview.chromium.org/100603004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238313 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238313