Re-enable some vulkan_content_browsertests

When ramping up SkiaRenderer + Vulkan coverage on Android we saw a high
rate of flakes around FeatureList startup. We disabled all tests that
saw this.

No other test has demonstrated this flake since, and a lot of development
of SkiaRenderer and Vulkan has occurred since. We are re-enabling these,
but will re-disable if new reproductions show up.

This affects the GPU FYI bot: 'Android FYI SkiaRenderer Vulkan (Pixel 2)'

TBR=backer@chromium.org
TEST= NavigationBrowserTest.HistoryBackCancelPendingNavigationUserGesture/1
      SitePerProcessBrowserTest.*
      TextFragmentAnchorBrowserTest.DisabledOnScriptNavigation/0
      vulkan_content_browsertests
Bug: 1012372

Change-Id: I4b6add8cec0eb4072000e09515916b928856676c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2097153Reviewed-by: Jonathan Ross <jonross@chromium.org>
Commit-Queue: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749367}

testing/buildbot/filters/gpu.skiarenderer_vulkan_content_browsertests.filter

-# FeatureList Flakes. https://crbug.com/1012372
--NavigationBrowserTest.HistoryBackCancelPendingNavigationUserGesture/1
+# TODO(jonross): Remove once Finch completes.
\ No newline at end of file
--SitePerProcessBrowserTest.*
--TextFragmentAnchorBrowserTest.DisabledOnScriptNavigation/0