Add a V8 benchmark suite run to test.py to catch failures on the buildbot.

tools/test.py

Index: tools/test.py
diff --git a/tools/test.py b/tools/test.py
index 939ca0c4928fe2c769e835144c7ce48e413c678a..66691ff738845322fe2fb60c5d96eeea005071a3 100755
--- a/tools/test.py
+++ b/tools/test.py
@@ -371,6 +371,9 @@ class TestCase(object):
   def AfterRun(self, result):
     pass
 
+  def GetCustomFlags(self, mode):
+    return None
+
   def Run(self):
     self.BeforeRun()
     try:
@@ -671,7 +674,10 @@ class Context(object):
     return [self.GetVm(mode)] + self.GetVmFlags(testcase, mode)
 
   def GetVmFlags(self, testcase, mode):
-    return testcase.variant_flags + FLAGS[mode]
+    flags = testcase.GetCustomFlags(mode)
+    if flags is None:
+      flags = FLAGS[mode]
+    return testcase.variant_flags + flags
 
   def GetTimeout(self, testcase, mode):
     result = self.timeout * TIMEOUT_SCALEFACTOR[mode]
@@ -1295,7 +1301,7 @@ def GetSpecialCommandProcessor(value):
     return ExpandCommand
 
 
-BUILT_IN_TESTS = ['mjsunit', 'cctest', 'message']
+BUILT_IN_TESTS = ['benchmarks', 'mjsunit', 'cctest', 'message']
 
 
 def GetSuites(test_root):