In WebRTC, we suddenly started getting a lot of content_browsertests failures in our https://build.chromium.org/p/chromium.webrtc.fyi/ waterfall. First failing run: https://build.chromium.org/p/chromium.webrtc.fyi/builders/Android%20Tests%20%28dbg%29%20%28K%20Nexus5%29/builds/9205

The reason is this Angle roll: https://codereview.chromium.org/2228553002 that removes the angle.isolate file: https://chromium-review.googlesource.com/#/c/365234/

Because of this, our tests started failing like this:
I    0.006s Main  command: /b/c/b/Android_Tests__dbg___L_Nexus6_/src/build/android/test_runner.py gtest --suite content_browsertests --isolate-file-path /b/c/b/Android_Tests__dbg___L_Nexus6_/src/out/Debug/gen.runtime/content/test/content_browsertests.device.isolate --output-directory /b/c/b/Android_Tests__dbg___L_Nexus6_/src/out/Debug --gtest_filter=WebRtc* --blacklist-file /b/c/b/Android_Tests__dbg___L_Nexus6_/src/out/bad_devices.json --verbose --isolate_file_path=/b/c/b/Android_Tests__dbg___L_Nexus6_/src/content/content_browsertests.isolate --flakiness-dashboard-server=test-results.appspot.com --json-results-file /tmp/tmpWfZUbv.json --adb-path /b/c/b/Android_Tests__dbg___L_Nexus6_/src/third_party/android_tools/sdk/platform-tools/adb
I    0.006s TimeoutThread-1-for-MainThread  [host]> /b/c/b/Android_Tests__dbg___L_Nexus6_/src/third_party/android_tools/sdk/platform-tools/adb devices
I    0.010s Main  [host]> /b/c/b/Android_Tests__dbg___L_Nexus6_/src/third_party/android_tools/sdk/build-tools/23.0.1/aapt dump xmltree /b/c/b/Android_Tests__dbg___L_Nexus6_/src/out/Debug/content_browsertests_apk/content_browsertests-debug.apk AndroidManifest.xml
I    0.089s Main  [host]> /usr/bin/python /b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/isolate.py remap --isolate /b/c/b/Android_Tests__dbg___L_Nexus6_/src/content/content_browsertests.isolate --isolated /b/c/b/Android_Tests__dbg___L_Nexus6_/src/out/Debug/content_browsertests.isolated --outdir /tmp/tmpi17Ysh --path-variable DEPTH /b/c/b/Android_Tests__dbg___L_Nexus6_/src --path-variable PRODUCT_DIR /b/c/b/Android_Tests__dbg___L_Nexus6_/src/out/Debug --config-variable use_ozone 0 --config-variable msvs_version 0 --config-variable v8_use_external_startup_data 1 --config-variable branding Chromium --config-variable chromeos 0 --config-variable tsan 0 --config-variable kasko 0 --config-variable msan 0 --config-variable use_x11 0 --config-variable component static_library --config-variable CONFIGURATION_NAME Debug --config-variable use_instrumented_libraries 0 --config-variable use_prebuilt_instrumented_libraries 0 --config-variable icu_use_data_file_flag 1 --config-variable asan 0 --config-variable lsan 0 --config-variable enable_pepper_cdms 0 --config-variable use_custom_libcxx 0 --config-variable enable_plugins 0 --config-variable fastbuild 0 --config-variable OS android --config-variable target_arch arm
C    0.978s Main  STDERR: Traceback (most recent call last):
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/isolate.py", line 1226, in <module>
    sys.exit(main(sys.argv[1:]))
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/isolate.py", line 1212, in main
    return dispatcher.execute(parser, argv)
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/third_party/depot_tools/subcommand.py", line 251, in execute
    return command(parser, args[1:])
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/isolate.py", line 974, in CMDremap
    complete_state = load_complete_state(options, cwd, None, options.skip_refresh)
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/isolate.py", line 677, in load_complete_state
    options.extra_variables, options.blacklist, options.ignore_broken_items)
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/isolate.py", line 506, in load_isolate
    self.saved_state.config_variables))
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/isolate_format.py", line 649, in load_isolate_for_config
    isolate = load_isolate_as_config(isolate_dir, eval_content(content), None)
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/isolate_format.py", line 627, in load_isolate_as_config
    included = load_included_isolate(isolate_dir, include)
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/isolate_format.py", line 557, in load_included_isolate
    None)
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/isolate_format.py", line 627, in load_isolate_as_config
    included = load_included_isolate(isolate_dir, include)
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/isolate_format.py", line 553, in load_included_isolate
    with fs.open(included_isolate, 'r') as f:
  File "/b/c/b/Android_Tests__dbg___L_Nexus6_/src/tools/swarming_client/utils/fs.py", line 120, in open
    return __builtin__.open(extend(path), *args, **kwargs)
IOError: [Errno 2] No such file or directory: '/b/c/b/Android_Tests__dbg___L_Nexus6_/src/third_party/angle/angle.isolate'

All our Chromium bots are using GN now, but it appears unexpected behavior is caused by that they still pass the --isolate_file_path flag, like this:
--isolate_file_path=/b/c/b/Android_Tests__dbg___K_Nexus5_/src/content/content_browsertests.isolate

jbudorick/agrieve: Can you update the test runner scripts so a clear error is thrown about it being deprecated (or just remove it entirely)?