Roll src/third_party/angle/ 6bc264aee..59c5b897e (4 commits)

https://chromium.googlesource.com/angle/angle.git/+log/6bc264aee686..59c5b897ec70

$ git log 6bc264aee..59c5b897e --date=short --no-merges --format='%ad %ae %s'
2018-04-03 oetuaho Validate gl_FragData and gl_FragColor access after parsing
2018-03-30 jmadill Vulkan: Make RenderTargetVk use ImageHelper.
2018-03-29 lucferron Vulkan: Support for bools and bvec* uniforms
2018-03-30 jmadill Vulkan: Add an Image helper class.

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;master.tryserver.chromium.win:win_optional_gpu_tests_rel
TBR=fjhenigman@chromium.org

Change-Id: I4f17f987277a23d4c13bb56dbeccf3482839b176
Reviewed-on: https://chromium-review.googlesource.com/995954Reviewed-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@{#548083}

DEPS

@@ -94,7 +94,7 @@ 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': '6bc264aee686a8b814e4be1f49e25f1443151c48',
+  'angle_revision': '59c5b897ec7068e13ba876b791933b5a64ec9de9',
   # 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.