[devtools] Don't install coverage gutter before source code has loaded
[devtools] Don't install coverage gutter before source code has loaded

When using the coverage reload feature, gutter installation could fail
due to a race condition between code loading having not finished yet,
and the coverage decoration manager trying to install gutters.

Bug: chromium:1000155
Change-Id: I45d0c9af3d1639a396865d5486de19d0168d7a48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787319
Commit-Queue: Sigurd Schneider <f04d242e109628a27a0f75fd49a87722bcf291fd@chromium.org>
Reviewed-by: Alexei Filippov <52e51c43e283548b762e3c9dd9a4600768db9fb4@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#694184}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 14958cd237ce34c3a814b21957b6f65ecc757521

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend