Roll src/third_party/angle/ c71862aa3..915864946 (2 commits)

https://chromium.googlesource.com/angle/angle.git/+log/c71862aa324c..91586494675e

$ git log c71862aa3..915864946 --date=short --no-merges --format='%ad %ae %s'
2017-12-20 bryan.bernhart Allow MapResource to return context loss GL error
2018-01-04 jmadill Entry Points: Auto-generate extensions EPs.

Created with:
  roll-dep src/third_party/angle


The AutoRoll server is located here: https://angle-chromium-roll.skia.org

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.


CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
TBR=jmadill@chromium.org

Change-Id: Icf7c500acef93be0db40a218287790155abb2fbf
Reviewed-on: https://chromium-review.googlesource.com/850441Reviewed-by: angle-deps-roller . <angle-deps-roller@chromium.org>
Commit-Queue: angle-deps-roller . <angle-deps-roller@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527092}

DEPS

@@ -90,7 +90,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling ANGLE
   # and whatever else without interference from each other.
-  'angle_revision': 'c71862aa324c4a7fd9f397cd770a509c1f576ec2',
+  'angle_revision': '91586494675e96468254f21acf05f6ad27d0d22b',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling build tools
   # and whatever else without interference from each other.