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/extensions

This CL was uploaded by git cl split.

[email protected]

Bug: 1018667
Change-Id: I086571be2512e726282a47d3f957beeb8d6a0dd4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917761
Auto-Submit: Mikel Astiz <[email protected]>
Reviewed-by: Finnur Thorarinsson <[email protected]>
Commit-Queue: Mikel Astiz <[email protected]>
Cr-Commit-Position: refs/heads/master@{#716023}
1 file changed