Roll src/third_party/devtools-frontend/src 7b9a9186c365..4b6a26740234 (2 commits)

https://chromium.googlesource.com/devtools/devtools-frontend.git/+log/7b9a9186c365..4b6a26740234

git log 7b9a9186c365..4b6a26740234 --date=short --first-parent --format='%ad %ae %s'
2019-12-03 changhaohan@chromium.org Leverage CDP error signal for timezone emulation
2019-12-03 aerotwist@chromium.org Migrates js_main/ to esm

Created with:
  gclient setdep -r src/third_party/devtools-frontend/src@4b6a26740234

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/devtools-frontend-chromium
Please CC devtools-waterfall-sheriff-onduty@grotations.appspotmail.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: chromium:1006759
Tbr: devtools-waterfall-sheriff-onduty@grotations.appspotmail.com
Change-Id: I49affd5ee94615497c04148a5a75c01f792e2003
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1948970Reviewed-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@{#721058}

DEPS

@@ -243,7 +243,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling devtools-frontend
   # and whatever else without interference from each other.
-  'devtools_frontend_revision': '7b9a9186c365c4a05de0eedfa5f8399752e538dc',
+  'devtools_frontend_revision': '4b6a267402341bd36948fc0adad68840df61b3ca',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling libprotobuf-mutator
   # and whatever else without interference from each other.