Do not instantiate base::FieldTrialList explicitly in tests

The test suite already instantiates a FieldTrialList as per
https://chromium-review.googlesource.com/c/chromium/src/+/1883567 so
it's no longer necessary to do so explicitly in tests.

This patch addresses unit tests under:
/chrome/browser/chrome_content_browser_client_unittest.cc

This CL was uploaded by git cl split.

Bug: 1018667
Change-Id: I08e044ff1aac9d05677a3041f5f757dca61124ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1916870
Auto-Submit: Mikel Astiz <[email protected]>
Reviewed-by: Marc Treib <[email protected]>
Commit-Queue: Marc Treib <[email protected]>
Cr-Commit-Position: refs/heads/master@{#715255}
1 file changed