Separate text fragment browsertests

These have grown large enough that it makes sense to split them out from
navigation browser tests into their own separate file.

This CL is a straightforward move with not changes to the tests
themselves.

Bug: None
Change-Id: Iba4759b4e8f5797d5a693775684312c8997bac12
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2160325Reviewed-by: Charlie Reis <creis@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#762141}

content/test/BUILD.gn

@@ -1066,6 +1066,7 @@ test("content_browsertests") {
     "../browser/sms/sms_browsertest.cc",
     "../browser/snapshot_browsertest.cc",
     "../browser/storage_partition_impl_browsertest.cc",
+    "../browser/text_fragment_browsertest.cc",
     "../browser/tracing/background_tracing_manager_browsertest.cc",
     "../browser/tracing/memory_instrumentation_browsertest.cc",
     "../browser/tracing/memory_tracing_browsertest.cc",