Should be able to scroll text in <input> fields with touch

Source/core/platform/ScrollableArea.cpp

Index: Source/core/platform/ScrollableArea.cpp
diff --git a/Source/core/platform/ScrollableArea.cpp b/Source/core/platform/ScrollableArea.cpp
index 0f02cf04bc2b3ff3a325ea00e11de5e29b5a5752..e9b61b322938f98a72470364ee7ed115be568800 100644
--- a/Source/core/platform/ScrollableArea.cpp
+++ b/Source/core/platform/ScrollableArea.cpp
@@ -82,6 +82,21 @@ void ScrollableArea::setScrollOrigin(const IntPoint& origin)
     }
 }
 
+bool ScrollableArea::touchScroll(ScrollDirection direction, ScrollGranularity granularity, float multiplier)

[Rick Byers, 2013/05/30 16:15:00]

Adding a new method for this feels wrong to me (as does the duplication of code
here).

Can't we just handle this case inside of 'scroll'?  Eg. maybe
horizontalScrollbar returns null or a dummy value, then we fall back to
scrollbar-less scrolling behavior.

[Rick Byers, 2013/05/30 16:15:00]

This is called 'touchScroll' but there's nothing in the code that limits it to
touch.  After playing with it, I actually kind of like how this behaves with the
trackpad and horiz mousewheel - seems like a nice feature there too, but not as
essential as the touchscreen.

We should probably check with jamesr to see what he thinks.  If letting trackpad
scroll here too is what we want then we need tests for the other input cases as
well.

[bokan, 2013/05/30 18:23:51]

That's what I tried at first, but that breaks non-scrollable divs since they
indicate they're non-scrollable by lack of Scrollbar. I also tried giving the
div an "invisible scrollbar" but that seemed much more heavy-weight and risky.

The other option is to add a flag parameter to scroll, something like "bool
forceScroll" that forces the scroll to occur even in the absence of scrollbars.
Thoughts? 

+{
+    // For a touch scroll, we don't need the scrollbars to exist (i.e. for an input text field)
+    ScrollbarOrientation orientation;
+    if (direction == ScrollUp || direction == ScrollDown)
+        orientation = VerticalScrollbar;
+    else
+        orientation = HorizontalScrollbar;
+
+    if (direction == ScrollUp || direction == ScrollLeft)
+        multiplier = -multiplier;
+
+    return scrollAnimator()->scroll(orientation, granularity, 1.0f, multiplier);

[Rick Byers, 2013/05/30 16:15:00]

Is treating all values of 'granularity' really ok?  How might a value other than
ScrollByPixel/ScrollByPrecisePixel get here?

[bokan, 2013/05/30 18:23:51]

In theory, it looks like a wheel could send a non-pixel granularity but the
horizontal wheel I tried sends pixel granularity. In that case the size of the
scroll is controlled by the multiplier parameter (6.0 for wheel when I tested).
Otherwise it looks like it should always be pixel granularity.

+}
+
 bool ScrollableArea::scroll(ScrollDirection direction, ScrollGranularity granularity, float multiplier)
 {
     ScrollbarOrientation orientation;