ref: Implement trace control in javascript.

This CL includes logic to properly control setting the trace flags
in javascript.  You can also control tracing by setting a regular
expression to match span names and annotations.  I still need
to add some tests.

Change-Id: I3a1d3a6a4652462d9fc93e2c88e170881005bea8
MultiPart: 2/3
5 files changed