run_test_cases.py: Enable use of RUN_TEST_CASES_RESULT_FILE as environment variable.

tools/isolate/run_test_cases_test.py

Index: tools/isolate/run_test_cases_test.py
diff --git a/tools/isolate/run_test_cases_test.py b/tools/isolate/run_test_cases_test.py
index b0b56368dac3067645d97742fdd548d83187688c..c676ba390486b4988d86d45734177227d7a4802e 100755
--- a/tools/isolate/run_test_cases_test.py
+++ b/tools/isolate/run_test_cases_test.py
@@ -99,12 +99,12 @@ class RunTestCases(unittest.TestCase):
   def test_gtest_filter(self):
     old = run_test_cases.run_test_cases
     exe = os.path.join(ROOT_DIR, 'data', 'gtest_fake', 'gtest_fake_pass.py')
-    def expect(executable, test_cases, jobs, timeout, no_dump):
+    def expect(executable, test_cases, jobs, timeout, result_file):
       self.assertEquals(exe, executable)
       self.assertEquals(['Foo.Bar1', 'Foo.Bar3'], test_cases)
       self.assertEquals(run_test_cases.num_processors(), jobs)
       self.assertEquals(120, timeout)
-      self.assertEquals(None, no_dump)
+      self.assertEquals(exe + '.run_test_cases', result_file)
       return 89
     try:
       run_test_cases.run_test_cases = expect