Introduce SourceLocation to be used for console messages.

SourceLocation is meant to be used instead of ScriptCallStack and beyond,
representing a location which triggered something (e.g. a console message).

BUG=613882

Review-Url: https://codereview.chromium.org/1997293002
Cr-Commit-Position: refs/heads/master@{#395539}
20 files changed