Extended end of timeline to account for all entries in the HAR.

Hi there,

The commits includes fixes to two problems I encountered:

1. Some HAR log entries may have an undefined mime-type field

  In those cases, the program bails out at controllers.js line 22. No entries are, then, displayed, leaving only the page load time summary (gray bar) on the screen. The quick fix categorizes those entries as "others" to allow processing to continue.

2. chromeHAR didn't always scale the timeline correctly

  Currently, chromeHAR walkes through log.pages array in the HAR to determine where the end of the timeline should be. This doesn't work very well for pages that perform async data requests after the page loads. The fix iterates through each of the entries included in the HAR to determine the relative load time of the last entry and uses that as the end of the timeline instead.