Make the WebGL conformance tests run in 'quiet mode' to reduce runtime
Make the WebGL conformance tests run in 'quiet mode' to reduce runtime

I found that WebGL conformance runtime on a Retina Mac could be reduced by
~3 minutes by preventing the tests from constantly updating the DOM with
"PASSED" messages, which the test harness doesn't pay any attention to anyway.

BUG=522234

Review URL: https://codereview.chromium.org/1308033005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#345470}

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