Fixed --browser flag for webgl_conformance with D3D9 and GL backends.
Fixed --browser flag for webgl_conformance with D3D9 and GL backends.

BUG=542370
TBR=thakis@chromium.org

Review URL: https://codereview.chromium.org/1569553003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#368053}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk