Improvements to stacktrace handler for constructors

This changeset improves the SourceRevealer for certain types of
stacktraces:

(1) Constructors. If your class initializes fields using code, these
    are logically grouped into the constructor, but the linenumbers do
    not fit the constructor source range. Before this CL, this would
    cause the revealer to show the constructor method rather than the
    field initialization line.

(2) Class initializers. If you clicked on a class initializer method,
    the IDE would throw an NPE. There's now some special handling to
    deal with these.

Change-Id: Ibb3b7dcf13a69018f75fd12648d1f6b5c45625cc