Fix bug in pyauto perf tests where list containing result 0 isn't handled properly.

chrome/test/functional/perf.py

Index: chrome/test/functional/perf.py
diff --git a/chrome/test/functional/perf.py b/chrome/test/functional/perf.py
index a7a8342062a29df1678f29cacf51c1003a6e2d7d..6314ea3849c41b8568f4a68c2f2a9ee31e11f9b0 100755
--- a/chrome/test/functional/perf.py
+++ b/chrome/test/functional/perf.py
@@ -376,14 +376,15 @@ class BasePerfTest(pyauto.PyUITest):
           are iteration numbers.  If this argument is specified, then the
           |value| argument must be a list of (x, y) tuples.
     """
-    if isinstance(value, list) and value[0] and isinstance(value[0], tuple):
+    if (isinstance(value, list) and value[0] is not None and
+        isinstance(value[0], tuple)):
       assert units_x
     if units_x:
       assert isinstance(value, list)
 
     if self.IsChromeOS():
       # ChromeOS results don't support lists.
-      if (isinstance(value, list) and value[0] and
+      if (isinstance(value, list) and value[0] is not None and
           not isinstance(value[0], tuple)):
         value = Mean(value)