Rolling 2 dependencies

shaderc landed a change to its API, which was a breaking change to Dawn. This CL
rolls both dependencies ahead so that the breakage and fix can be landed
together. Because these changes are in different repos, the autorollers will
never successfully pick up these changes, since it only updates one hash at a
time.

Roll src/third_party/dawn/ 785ec66b6..38b295de3 (20 commits)

https://dawn.googlesource.com/dawn.git/+log/785ec66b66a3..38b295de3851

$ git log 785ec66b6..38b295de3 --date=short --no-merges --format='%ad %ae %s'
2019-09-20 cwallez Fix availability check for MTLCopyAllDevices
2019-09-19 cwallez BUILD.gn: Delete stale generated files in Dawn's gen dir.
2019-09-19 rharrison Rolling 4 dependencies
2019-09-19 bryan.bernhart Check if allocation is valid before deallocating.
2019-09-19 rharrison Roll ahead shaderc API and update API usage as needed
2019-09-18 cwallez BUILD.gn: Add a check generated files are in allowed dirs.
2019-09-18 bryan.bernhart Remove device dependencies from ringbuffer.
2019-09-18 enga Fix leak of ErrorData after Device::ConsumedError
2019-09-18 cwallez Clarify disabled warning for Metal in BUILD.gn
2019-09-18 cwallez Normalize generated file paths to match main tree.
2019-09-18 cwallez Support compilation of Dawn on iOS.
2019-09-18 cwallez generator_lib.py: correctly handle lack of --jinja2-path.
2019-09-17 cwallez Add some missing headers in BUILD.gn files.
2019-09-17 cwallez Add missing include in the Vulkan backend.
2019-09-17 enga Add README.md for the Dawn perf test harness
2019-09-17 enga Support setting bind groups before pipeline for all backends
2019-09-17 natlee OpenGL: clear nonrenderable texture formats
2019-09-17 enga Support ErrorScopes for asynchronous GPU execution
2019-09-17 yunchao.he Fix a typo in viewport validation test
2019-09-17 hao.x.li Revert "Skip some end2end tests for Vulkan validation layers enable on Windows"

Roll src/third_party/shaderc/src/ 5903ef1f9..cb8b3fc5c (2 commits)

https://chromium.googlesource.com/external/github.com/google/shaderc.git/+log/5903ef1f95a0..cb8b3fc5caf9

$ git log 5903ef1f9..cb8b3fc5c --date=short --no-merges --format='%ad %ae %s'
2019-09-19 rharrison Rolling 6 dependencies and update known_failures (#809)
2019-09-18 rharrison Code hygiene work for spvc (#808)

Created with:
  roll-dep src/third_party/dawn src/third_party/shaderc/src

BUG=chromium:1006181

Change-Id: Ib2e4d69cbc87eba687025ff78a28c21e2681bd30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1815982
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#698596}

DEPS

@@ -293,11 +293,11 @@ 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.
-  'shaderc_revision': '5903ef1f95a0acdbbd3ae645af1a6d6b30320f10',
+  'shaderc_revision': 'cb8b3fc5caf99c54fba88ac3c0a45ed6e50c0f43',
   # 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': '785ec66b66a3577e4f17306a10ab30b7f92c49ae',
+  'dawn_revision': '38b295de38515b8e05ea0232c4732e4088110b16',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling feed
   # and whatever else without interference from each other.