WheelEvent's deltaX/deltaY sign is wrong

According to the specification, if a user agent scrolls as the default action
of the wheel event then the sign of the delta should be given by a right-hand
coordinate system where positive X, Y, and Z axes are directed towards the
right-most edge, bottom-most edge, and farthest depth (away from the user) of
the document, respectively:
http://www.w3.org/TR/DOM-Level-3-Events/#events-wheelevents

This signs for deltaX/deltaY are the inversed compared to the legacy
wheelDeltaX/wheelDeltaY. r156404 added support for DOM3 WheelEvent but used
the same sign for deltaX/deltaY and wheelDeltaX/wheelDeltaY.

Firefox 23 and IE10 uses the right sign according to the specification.

BUG=227454

Review URL: https://chromiumcodereview.appspot.com/22888005

git-svn-id: svn://svn.chromium.org/blink/trunk@156478 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove unused Frame* arguments from Pasteboard methods.

BUG=276565

Review URL: https://chromiumcodereview.appspot.com/23382002

git-svn-id: svn://svn.chromium.org/blink/trunk@156479 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Put step into selection feature behind the experiments

Review URL: https://chromiumcodereview.appspot.com/23328002

git-svn-id: svn://svn.chromium.org/blink/trunk@156480 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Added UMA instrumentation for site-instrumented user timing marks and measures

Added UMA histograms for each performance.mark (PLT.UserTiming_Mark) and merformance.measure (PLT.UserTiming_MeasureDuration) that were instrumented by pages.

Entry points were also exposed that measure the last mark on a page as well as if a page was instrumented for user timing so that the Chrome side of the code can report UMA's to track those.  The last mark (PLT.UserTiming_LastMark) is useful in cases where sites instrument a bunch of things they want to track and it lets you know when the last one of those happened (like all of the above-the-fold images finished loading).  Knowing if a page was instrumented (PLT.UserTiming_Instrumented) with user timing will let us track adoption over time.

The Chrome-side of the code will be uploaded after the blink patch lands and is included in the blink milestone used by Chrome.

BUG=262567

Review URL: https://chromiumcodereview.appspot.com/23245004

git-svn-id: svn://svn.chromium.org/blink/trunk@156481 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make scrollbar thumb thickness and margin configurable.

When using overlay scrollbars on desktop, remove the margin and
increase the width.  This makes them easier to see on desktop.
No visible changes to android.

BUG=274010
TEST=None

Review URL: https://chromiumcodereview.appspot.com/22815011

git-svn-id: svn://svn.chromium.org/blink/trunk@156482 bbb929c8-8fbe-4397-9dbb-9b2b20218538