Minor refactor to simplify code in content/test/test_content_client.cc
Minor refactor to simplify code in content/test/test_content_client.cc

Addresses review comments from caa7a3dddb27b19eb
BUG=505538

Review URL: https://codereview.chromium.org/1210153008

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#337393}

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