Fix bug where you can't click on first point of a trace.
Fix bug where you can't click on first point of a trace.

BUG=skia:5464

Change-Id: If41aae0efdb163ca4e34cf1fa3396cce83565d64
Reviewed-on: https://skia-review.googlesource.com/2501
Reviewed-by: Ben Wagner <3ef7217be91069877d94f7907ce5479000772cd3@google.com>
Commit-Queue: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot