Roll src/third_party/dawn 42e1bba480d1..ef2fac0b9447 (2 commits)

https://dawn.googlesource.com/dawn.git/+log/42e1bba480d1..ef2fac0b9447

git log 42e1bba480d1..ef2fac0b9447 --date=short --no-merges --format='%ad %ae %s'
2019-08-09 iannucci@google.com [infra/config] Bump OS X SDK version for dawn.
2019-08-09 enga@chromium.org MemoryTransferService: Separate functions to serialize and get serialization size

Created with:
  gclient setdep -r src/third_party/dawn@ef2fac0b9447

The AutoRoll server is located here: https://autoroll.skia.org/r/dawn-chromium-autoroll

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:dawn-linux-x64-deps-rel;luci.chromium.try:dawn-mac-x64-deps-rel;luci.chromium.try:dawn-win10-x64-deps-rel;luci.chromium.try:dawn-win10-x86-deps-rel
TBR=cwallez@google.com

Bug: chromium:973721
Change-Id: Ia452ea580eb976bdde546ba34ac9d0756276137d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1745321Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#685446}

DEPS

@@ -280,7 +280,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling feed
   # and whatever else without interference from each other.
-  'dawn_revision': '42e1bba480d1eebc9df9c39551711d3fd3d033aa',
+  'dawn_revision': 'ef2fac0b9447cb4cbb93616bc91508ffb6fef599',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling feed
   # and whatever else without interference from each other.