Remove blink web test dependency on --enable-blink-gen-property-trees

This patch switches web tests to use
--enable-blink-features=BlinkGenPropertyTrees instead of
--enable-blink-gen-property-trees. This will let us remove the BGPT-specific
command line flag in the future.

To run web tests (formerly layout tests) with BlinkGenPropertyTrees, use:
[run_web_tests] --additional-driver-flag=--enable-blink-features=BlinkGenPropertyTrees

Bug: 836884
Change-Id: Ie4fa7d4f8ed8b7c027d6c34308230a4735d77972
Reviewed-on: https://chromium-review.googlesource.com/c/1355610
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612683}
94 files changed