Add internals API for highlighting text markers and use it for SVG tests

This patch adds a new API to internals for highlighting text match
markers: setMarkedTextMatchesAreHighlighted. This turns on the
highlights on document markers which are normally enabled when searching
for a string via ctrl+f.

As a followup to r166368[1], I've converted an existing manual test
to an automated test.

[1] https://src.chromium.org/viewvc/blink?view=rev&revision=166368

BUG=56580

Review URL: https://codereview.chromium.org/154533002

git-svn-id: svn://svn.chromium.org/blink/trunk@166549 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix flakiness in fast/multicol/shrink-to-column-height-for-pagination.html.

setTimeout here is totally unnecessary.

Review URL: https://codereview.chromium.org/151843009

git-svn-id: svn://svn.chromium.org/blink/trunk@166550 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove CheckFocusedElementTask

Previously, we'd spin posting the CheckFocusedElementTask waiting for style
recalc and layout to occur.  After this CL, we check whether the focused element
is no longer focusable at the end of recalc style.  We still fire the blur events
asynchronously, however.

BUG=340455

Review URL: https://codereview.chromium.org/155433003

git-svn-id: svn://svn.chromium.org/blink/trunk@166551 bbb929c8-8fbe-4397-9dbb-9b2b20218538