Fix performance trybots.

tools/run-bisect-perf-regression.py

Index: tools/run-bisect-perf-regression.py
diff --git a/tools/run-bisect-perf-regression.py b/tools/run-bisect-perf-regression.py
index 7a1669799b4916823949a40c7a05b213793902ff..58edfc80e9d51b8166c113590ef452a87af527b6 100755
--- a/tools/run-bisect-perf-regression.py
+++ b/tools/run-bisect-perf-regression.py
@@ -270,8 +270,13 @@ def _RunPerformanceTest(config, path_to_file):
   bisect_utils.OutputAnnotationStepClosed()
 
   bisect_utils.OutputAnnotationStepStart('Reverting Patch')
-  if bisect_utils.RunGClient(['revert']):
-    raise RuntimeError('Failed to run gclient runhooks')
+  # TODO: When this is re-written to recipes, this should use bot_update's
+  # revert mechanism to fully revert the client. But for now, since we know that
+  # the perf trybot currently only supports src/ and src/third_party/WebKit, we
+  # simply reset those two directories.
+  bisect_utils.CheckRunGit(['reset', '--hard'])
+  bisect_utils.CheckRunGit(['reset', '--hard'],
+                           os.path.join('third_party', 'WebKit'))
   bisect_utils.OutputAnnotationStepClosed()
 
   bisect_utils.OutputAnnotationStepStart('Building Without Patch')