Removing --disable/enable-threaded-compositing cmdline switches.

Removing --disable/enable-threaded-compositing cmdline switches.

Threaded compositing is the default behavior (chrome's renderers will
crash with --disable-threaded-compositing and content_shell will
display blank/white web contents).  Therefore, this CL removes
the related cmdline switches and moves layout tests to always work with
threaded compositing.  This helps to
1) test what we ship (and not some other, test-only mode)
2) unblocks getting browser-side, OOPIF-friendly pixel-dumps
   (see https://crbug.com/667551#c5).

BUG=738089
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

[Łukasz Anforowicz, 2017-06-29 20:03:14]

Description was changed from

==========
Removing --disable/enable-threaded-compositing cmdline switches.

Threaded compositing is the default behavior (chrome's renderers will
crash with --disable-threaded-compositing and content_shell will
display blank/white web contents).  Therefore, this CL removes
the related cmdline switches and moves layout tests to always work with
threaded compositing.  This helps to
1) test what we ship (and not some other, test-only mode)
2) unblocks getting browser-side, OOPIF-friendly pixel-dumps
   (see https://crbug.com/667551#c5).

BUG=738089
==========

to

==========
Removing --disable/enable-threaded-compositing cmdline switches.

Threaded compositing is the default behavior (chrome's renderers will
crash with --disable-threaded-compositing and content_shell will
display blank/white web contents).  Therefore, this CL removes
the related cmdline switches and moves layout tests to always work with
threaded compositing.  This helps to
1) test what we ship (and not some other, test-only mode)
2) unblocks getting browser-side, OOPIF-friendly pixel-dumps
   (see https://crbug.com/667551#c5).

BUG=738089
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

[Łukasz Anforowicz, 2017-06-29 20:03:22]

The CQ bit was checked by lukasza@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-06-29 20:03:43]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-06-29 21:10:39]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-06-29 21:10:40]

Dry run: Try jobs failed on following builders:
  linux_chromium_rel_ng on master.tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)