DevTools: re-use sources_test_runner in debugger-test.js

debugger-test.js becomes a simple script to load sources_test_runner
module in order to reuse code between the legacy and new test frameworks.

Note: Some of the UI source code counts incremented by 2 because they are 
two new anonymous scripts from sources_test_runner initAsync calls.

Bug: 667560
Change-Id: I5232ad1a8e8aa2eafd9b0666793195c4d5742bc4
Reviewed-on: https://chromium-review.googlesource.com/716537
Commit-Queue: Will Chen <chenwilliam@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508617}
21 files changed