Telemetry: Use the leftmost argument to find the test to parse flags.
Telemetry: Use the leftmost argument to find the test to parse flags.

Previously it would check all of the arguments, and use the last test found.
This is causes problems as different tests can be used to create the parser and
accepts the parsed flags.

SHERIFFS: If errors related to parsing flags for run_measurement, run_benchmark
or run_gpu_test.py appear, this is likely the cause. It is safe to revert.

BUG=413334

Review URL: https://codereview.chromium.org/582793002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#295738}

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