Roll third_party/externals/dawn 275a95c1dc64..949f1e45f1dc (4 commits)

https://dawn.googlesource.com/dawn.git/+log/275a95c1dc64..949f1e45f1dc

git log 275a95c1dc64..949f1e45f1dc --date=short --first-parent --format='%ad %ae %s'
2020-05-19 natlee@microsoft.com Refactor MapRequestTracker to be its own class file.
2020-05-19 jiawei.shao@intel.com Disallow the copies within the same buffer
2020-05-18 hugo.amiard@laposte.net D3D12: Implement UseDxc toggle to use DXC for HLSL compilation
2020-05-18 bryan.bernhart@intel.com D3D12: De-duplicate sampler heap allocations.

Also rolling transitive DEPS:
  https://chromium.googlesource.com/chromium/src/third_party/jinja2 b41863e42637..b41863e42637
  https://chromium.googlesource.com/chromium/src/third_party/markupsafe 8f45f5cfa000..8f45f5cfa000
  https://chromium.googlesource.com/external/github.com/KhronosGroup/glslang 4fa68edd6819..4fa68edd6819
  https://chromium.googlesource.com/external/github.com/google/shaderc 00ac5d82178c..00ac5d82178c

Created with:
  gclient setdep -r third_party/externals/dawn@949f1e45f1dc

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/dawn-skia-autoroll
Please CC cwallez@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

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

Bug: None
Tbr: cwallez@google.com
Change-Id: I91695d198525221fa0ef681cad960e7cb3280f6f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/290707
Reviewed-by: skia-autoroll <skia-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: skia-autoroll <skia-autoroll@skia-public.iam.gserviceaccount.com>
1 file changed