Fix check for new v8 pushes to trunk from bleeding_edge.

So it turned out that the "Prepare push to trunk" isn't guaranteed anymore, so the new v8 mapping to bleeding edge wasn't quite right.

BUG=
NOTRY=true

Review URL: https://codereview.chromium.org/218083002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@261449 0039d316-1c4b-4281-b951-d872f2087c98

tools/bisect-perf-regression.py

@@ -1172,6 +1172,7 @@ class BisectPerformanceMetrics(object):
             git_revision = self.source_control.ResolveToRevision(
                 bleeding_edge_revision, 'v8_bleeding_edge', 1,
                 cwd=v8_bleeding_edge_dir)
+            return git_revision
           except IndexError, ValueError:
             pass