[DevTools] fixed crash on stepIntoAsync fetch
[DevTools] fixed crash on stepIntoAsync fetch

Network should not be intsrumented with JavaScript AsyncTask
instrumentation since it does not trigger JS execution explicitly.

R=e1161d7019a0d5c7981e3c3ffc69c76f4b09679a@chromium.org

Bug: chromium:840502
Change-Id: I07a939b7f583b0330fa40afb0326a40e58918547
Reviewed-on: https://chromium-review.googlesource.com/1049107
Commit-Queue: Aleksey Kozyatinskiy <562acbea96970f508ad9f5cc9fc7c62d82dd3ef8@chromium.org>
Commit-Queue: Pavel Feldman <e1161d7019a0d5c7981e3c3ffc69c76f4b09679a@chromium.org>
Reviewed-by: Pavel Feldman <e1161d7019a0d5c7981e3c3ffc69c76f4b09679a@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#556673}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: af27f53e066caf431f7999c9069aca1c4f374f62
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