DevTools: set highlighter type on binding change

This gets the highlighter type from the network UISourceCode, if it
exists. For overrides files with no extension, they will stay colorful
as long as they are bound.

Change-Id: I5f1ff41f54eabb7a7f1abf1aa27b19629529fbfd
Reviewed-on: https://chromium-review.googlesource.com/1003875
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Reviewed-by: Andrey Lushnikov <lushnikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549683}
6 files changed