Add error handling of beginRecording
Add error handling of beginRecording

- End recording when the chrome://tracing window is closed or reloaded,
  otherwise we can't start tracing again.
- Handle '##ERROR##' from /json/categories and /json/begin_recording
  requests (required a C++ side change). This will popup an error box
  if tracing is started from the second chrome://tracing window while
  the first chrome://tracing window is tracing.

BUG=chromium:331286
R=nduca@chromium.org

Review URL: https://codereview.appspot.com/47660043

git-svn-id: 3a56fcae908c7e16d23cb53443ea4795ac387cf2@1084 0e6d7f2b-9903-5b78-7403-59d27f066143

bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer