Fix a -Wswitch warning in ANGLE.
Fix a -Wswitch warning in ANGLE.

BUG=505308

Change-Id: I34ae3aa65ce55c4e04eecfef3c9cde9841e47140
Reviewed-on: https://chromium-review.googlesource.com/288245
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Tested-by: Daniel Cheng <16123c1b20e8652874389dd38d18c4766d539508@chromium.org>

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