Standardize on "Gecko" + filename as the log tag for
each file. Strip "Gecko" from the front of the filename
if it already starts with "Gecko". This allows grepping
for either the filename or Gecko in logcat output.
Add a session history listener to gecko so that session navigation
events can be listened for. This allows us to detect when javascript
code calls history.back() and related functions, and updates the
history state on the Java side accordingly.
