Simplify TurboFan's c1visualizer file handling.

Simplify TurboFan's c1visualizer file handling.

Still having GetTurboCfgFileName in Isolate is ugly, but if we decide that we
don't want to truncate the output file (which would be consistent with
--trace-hydrogen), this could be moved to TurboCfgFile where it actually
belongs.

R=bmeurer@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=24819

[Sven Panne, 2014-10-22 09:52:51]

svenpanne@chromium.org changed reviewers:
+ bmeurer@chromium.org

[Benedikt Meurer, 2014-10-23 07:22:19]

lgtm

[Sven Panne, 2014-10-23 07:26:23]

Committed patchset #1 (id:1) manually as 24819 (presubmit successful).