Gardening: Expand virtual/threaded/animations expectations on Linux.

The following tests are marked Pass Timeout on Mac:

animation-direction-reverse-fill-mode.html
animation-direction-reverse-fill-mode-hardware.html

After r156414/Chromium r218597 these are also flakily timing out on
Linux.

BUG=248938
TBR=ccameron@chromium.org

Review URL: https://codereview.chromium.org/22935017

git-svn-id: svn://svn.chromium.org/blink/trunk@156431 bbb929c8-8fbe-4397-9dbb-9b2b20218538
MediaDocumentParser should not call dispatchDocumentElementAvailable before the document element exists

When I switched MediaDocumentParser to use AttachLazily I made it call this notification
before the document element was appended. This reorders the function so it's called
at the right time. I don't think this is observable since nothing in Chromium ever
uses this hook for media documents.

Review URL: https://chromiumcodereview.appspot.com/23288006

git-svn-id: svn://svn.chromium.org/blink/trunk@156432 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Split FrameView::layout into pieces in hope that someday mere mortals can understand what it's trying to do

There should be no functional change.  (Other than one ASSERT_NOT_REACHED() I added to a branch with a FIXME that I think either we don't hit, or is wrong.)  I'm just moving code out of the gigantic layout() function and into (hopefully) appropriately named helper functions.

The split isn't perfect.  I introduced a new concept of "prelayout tasks"
mirroring the existing "postlayout tasks".  prelayout tasks are largely
code which doesn't even belong in layout(), but rather should be ensured
to be complete by whoever is actually making the layout() call.

Eventually I'd like to make FrameView::layout private and have a
another (smaller) object orchestrate the various stages of render tree construction.

Review URL: https://chromiumcodereview.appspot.com/23012007

git-svn-id: svn://svn.chromium.org/blink/trunk@156433 bbb929c8-8fbe-4397-9dbb-9b2b20218538
TextTrackRegion and MediaControlTextTrackContainerElement should use AttachLazily

Review URL: https://chromiumcodereview.appspot.com/23343002

git-svn-id: svn://svn.chromium.org/blink/trunk@156434 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Gardening: image-zoom-to-25.html is flaky.

This test has been flaky since birth in r156402 on Linux.

BUG=276759
TBR=tony@chromium.org

Review URL: https://codereview.chromium.org/23004007

git-svn-id: svn://svn.chromium.org/blink/trunk@156435 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Gardening: image-zoom-to-500.html is also flaky on Linux.

BUG=276759
TBR=tony@chromium.org

Review URL: https://codereview.chromium.org/22866016

git-svn-id: svn://svn.chromium.org/blink/trunk@156437 bbb929c8-8fbe-4397-9dbb-9b2b20218538