Reland of Stop silently accepting unsupported flags in test binaries (patchset #1 id:1 of https://codereview.webrtc.org/3002963002/ )

Reason for revert:
Relanding without changes.
Problem with unused flags was fixed in
https://codereview.webrtc.org/2998143002/

Original issue's description:
> Revert of Stop silently accepting unsupported flags in test binaries (patchset #5 id:150001 of https://codereview.webrtc.org/2968003003/ )
>
> Reason for revert:
> Causes failures on perf bots
> https://luci-milo.appspot.com/buildbot/client.webrtc.perf/Mac%2010.11/3567
>
> Original issue's description:
> > Stop silently accepting unsupported flags in test binaries
> >
> > Instead explicitly ignore only the flags we know should be ignored.
> >
> > BUG=webrtc:7568
> >
> > Review-Url: https://codereview.webrtc.org/2968003003
> > Cr-Commit-Position: refs/heads/master@{#19412}
> > Committed: https://chromium.googlesource.com/external/webrtc/+/a2782f6f5d350e423b8166d603f44e17e1d7540b
>
> TBR=kjellander@webrtc.org,henrika@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:7568
>
> Review-Url: https://codereview.webrtc.org/3002963002
> Cr-Commit-Position: refs/heads/master@{#19413}
> Committed: https://chromium.googlesource.com/external/webrtc/+/d64072c598875cdf3a8ce5806d3410125363596d

TBR=kjellander@webrtc.org,henrika@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:7568

Review-Url: https://codereview.webrtc.org/2999383002
Cr-Commit-Position: refs/heads/master@{#19455}
diff --git a/tools_webrtc/valgrind/webrtc_tests.py b/tools_webrtc/valgrind/webrtc_tests.py
index 627025c..dcd88e8 100755
--- a/tools_webrtc/valgrind/webrtc_tests.py
+++ b/tools_webrtc/valgrind/webrtc_tests.py
@@ -24,6 +24,7 @@
 specific suppressions in our own files.
 """
 
+import argparse
 import logging
 import optparse
 import os
@@ -124,6 +125,15 @@
                     help="run the tests with --test-launcher-shard-index")
   options, args = parser.parse_args()
 
+  ignore_parser = argparse.ArgumentParser()
+  # Ignore Chromium-specific flags
+  # TODO(oprypin): Remove (bugs.webrtc.org/8115)
+  ignore_parser.add_argument('--isolated-script-test-output',
+                             type=str, default=None)
+  ignore_parser.add_argument('--isolated-script-test-chartjson-output',
+                             type=str, default=None)
+  _, args = ignore_parser.parse_known_args(args)
+
   if options.verbose:
     logging_utils.config_root(logging.DEBUG)
   else: