Fix run_multiple_telemetry_benchmarks_as_googletest.py compile targets

https://build.chromium.org/p/chromium.perf.fyi/builders/One%20Buildbot%20Step%20Test%20Builder
is failing because the isolate target isn't being built on Linux Builder.

Bug: 758630
Change-Id: I793fed5a265b21762ba0a0cb6a669a3ba79f7ef6
Reviewed-on: https://chromium-review.googlesource.com/683462Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Stephen Martinis <martiniss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504500}

testing/scripts/run_multiple_telemetry_benchmarks_as_googletest.py

@@ -100,7 +100,9 @@ def main():
 # This is not really a "script test" so does not need to manually add
 # any additional compile targets.
 def main_compile_targets(args):
-  json.dump([], args.output)
+  # Force compilation of the new isolate. Will change to telemetry_perf_tests
+  # once we switch the main isolate over to running this file.
+  json.dump(['telemetry_perf_tests_new'], args.output)
 
 
 if __name__ == '__main__':