According to Source Map specification [1] source map url can be passed either as a magic comment at the end of script or as SourceMap http header. We already parse the former value and expose it on Script object. This change allows to unify the way we deal with source map urls received in http header by providing api for passing that url into the script being compiled.

source_map_url is intentionally not passed into CompilationCacheScript::Lookup. The cache is anyways disabled when debugger is on.

[1] https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit

LOG=Y
BUG=chromium:462572

Review URL: https://codereview.chromium.org/983603003

Cr-Commit-Position: refs/heads/master@{#27017}