Revert 158116 "DevTools: Speedup sourceURL matching"

Limiting SourceMappingURL to 1000 last characters is too conservative.

> DevTools: Speedup sourceURL matching
> 
> Do not use RegularExpression for sourceURL matching as creation of
> a regular expression takes time.
> 
> BUG=289714
> 
> Review URL: https://chromiumcodereview.appspot.com/24198005

TBR=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/25051002

git-svn-id: svn://svn.chromium.org/blink/trunk@158441 bbb929c8-8fbe-4397-9dbb-9b2b20218538