Roll src/third_party/angle/ 56c8577b4..a912046dc (5 commits)

https://chromium.googlesource.com/angle/angle.git/+log/56c8577b4dbf..a912046dc3e1

$ git log 56c8577b4..a912046dc --date=short --no-merges --format='%ad %ae %s'
2018-04-12 lucferron Vulkan: DrawElements with line loops client side memory support
2018-04-10 lucferron Vulkan: Lineloops edge base bugfix and new tests
2018-04-12 jmadill ImageIndex: Consolidate layer/cube face.
2018-03-20 courtneygo Add json build file generation
2018-04-09 lfy GLES1: Built-in matrix operations

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=luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
TBR=ynovikov@chromium.org

Change-Id: Ifbb5896b025022f9abc261f14ccce9355965fbcd
Reviewed-on: https://chromium-review.googlesource.com/1011263Reviewed-by: angle-chromium-autoroll <angle-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Commit-Queue: angle-chromium-autoroll <angle-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#550756}

DEPS

@@ -98,7 +98,7 @@ 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': '56c8577b4dbf2239780e38090dadbeb06f4b8563',
+  'angle_revision': 'a912046dc3e1dd1fb53cc18b438e7b6b11d6dc25',
   # 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.