Add report dialog with ability to download the report.

The report consists of a set of events and aims to writting a log file
compatible with chrome devtools. Note that besides explicitly logged
events with traceEventInstance, console.log and window.onerror are also
logged into the report.
Clean pull request of unused code and JS quote style.
Adding traceEventInstant to tests.
Indented html.
Merge pull request #283 from GoogleChrome/testrtc-report

Add report dialog with ability to download the report.