Roll DEPS for shaderc and dawn

There is a breaking API change in shaderc, so these need to be rolled
together to have the break and fix land atomically. The autorollers
will not successfully roll either of these repos independently.

Change-Id: I75633ce8826c6698cd65a6d99c600111e76ca0d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1813919
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
Cr-Commit-Position: refs/heads/master@{#698105}

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': '68b6857ac09df396b51c740876654e9efca97f53',
   # 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': 'ae4dbeb178420e4088153069c2d6184b34d4d394',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling feed
   # and whatever else without interference from each other.