Revert "Use v8 Microtask Queue"

This reverts https://src.chromium.org/viewvc/blink?view=rev&revision=170386

Using V8's microtask queue to run Object.observe callbacks runs into
trouble because V8 doesn't know how to properly set up the notion of
an "entered" Context when invoking callbacks.

With this patch, Blink passes the test in https://codereview.chromium.org/232503006/.

See attached bug for more details.

BUG=360891

Review URL: https://codereview.chromium.org/233613002

git-svn-id: svn://svn.chromium.org/blink/trunk@171295 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[DevTools] Allow user agent override on remote frontend.

BUG=360031

Review URL: https://codereview.chromium.org/232783005

git-svn-id: svn://svn.chromium.org/blink/trunk@171296 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: report number of selection regions in editor statusbar

This patch adds information for number of selection regions in
editor statusbar.

Review URL: https://codereview.chromium.org/225393008

git-svn-id: svn://svn.chromium.org/blink/trunk@171297 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Block an invalid UTF-16 string from findPlainText

We should not pass an invalid UTF-16 input to ICU's
usearch_setPattern(). Blocking it on the ICU's end does not
help in terms of the efficiency (the same check has to be done but only
further down the code path.)

BUG=360431
TEST=1. webkit_unit_tests --gtest_filter=*findPlainTextInval*
2. Do the above with an ASAN build and it should not crash.

Review URL: https://codereview.chromium.org/229193002

git-svn-id: svn://svn.chromium.org/blink/trunk@171298 bbb929c8-8fbe-4397-9dbb-9b2b20218538