Call/memory tracing in the extension.
Buttons right in the WTF popup to instrument calls/memory! Woo! It only
supports synchronous appended script blocks right now, but that's most of
Maps.
This needs some code sharing work with the command line version (that
is still useful for other browsers), and a lot of performance improvements.
It also cannot capture all scripts and apps using it will need some
minor changes in their loaders.
Merge pull request #444 from google/extension_tracing

Call/memory tracing in the extension.