For breakpoints which are set by setBreakpointByUrl(url:..) backend calculates source hint on first related breakpoints resolved event and then uses this hint to adjust breakpoint position in later arrived scripts with the same url or on page reload.

Doc: https://docs.google.com/a/google.com/document/d/1VtWo_-jelzEXSNbjESGTtruZngzXgbHLexfTzxNlnjE/edit?usp=sharing

BUG=chromium:688776
R=pfeldman@chromium.org, alph@chromium.org

Review-Url: https://codereview.chromium.org/2671193002
Cr-Commit-Position: refs/heads/master@{#43493}