Allow packaging non-json trace data to HTML

In contrast to normal JSON trace data, Android systraces are stored in
a plain text format. Previously the trace2html script required
everything to be JSON, which made it impossible to package systraces
into an HTML file. This patch lifts that restriction.
Can you put a comment here that this is because we previously load'd the JSON data, so if we received JSON then this is a json object instead of string data?

Something along those lines.