Roll src/third_party/devtools-frontend/src a0a6e29dda17..4c9c7b71c881 (3 commits)

https://chromium.googlesource.com/devtools/devtools-frontend.git/+log/a0a6e29dda17..4c9c7b71c881

git log a0a6e29dda17..4c9c7b71c881 --date=short --first-parent --format='%ad %ae %s'
2019-12-17 aerotwist@chromium.org Adds test for measuredScrollbarWidth
2019-12-17 aerotwist@chromium.org Updates Karma paths
2019-12-17 janscheffler@chromium.org Add "copy as Node.js fetch" option to network log

Created with:
  gclient setdep -r src/third_party/devtools-frontend/src@4c9c7b71c881

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:1009443
Tbr: devtools-waterfall-sheriff-onduty@grotations.appspotmail.com
Change-Id: I3a7dcd7bca33f2c65b57c735b79869cc5bb04b71
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1971771Reviewed-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@{#725551}

DEPS

@@ -246,7 +246,7 @@ 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': 'a0a6e29dda1748661d814ade6c72a0da6202d1ff',
+  'devtools_frontend_revision': '4c9c7b71c88168c540ce7545092a0f603f2b109a',
   # 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.