Set test_path_format in run_gtest_benchmark.py

As discussed on the doc [1], adding a test_path_format option for correct
parsing of test paths. The testPath attribute is now mandatory, so
adding it to the test.

[1] https://docs.google.com/document/d/18PstJFR6kmEeDiQZjVzJaqXWm4SocuZXrFVu57xDm-4

Change-Id: Id988cd620da0927fab9fb42b81fd52855198f75c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1899625
Commit-Queue: Mikhail Khokhlov <khokhlov@google.com>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712659}

tools/perf/run_gtest_benchmark.py

@@ -82,7 +82,8 @@ def main(args):
   parser.add_argument('executable', help='The name of the executable to run.')
 
   options, leftover_args = parser.parse_known_args(args)
-  results_processor.ProcessOptions(options, standalone=True)
+  options.test_path_format = 'gtest'
+  results_processor.ProcessOptions(options)
 
   run_return_code = RunGTest(options, leftover_args)
   process_return_code = ProcessResults(options)

tools/perf/testdata/dummy_luci_test_result_template.json

 {
   "testResult": {
+    "testPath" : "DummySuite.DummyCase",
     "status": "PASS",
     "expected": true,
     "outputArtifacts":{