tweak snap scroll
tweak snap scroll

WebView.mHeldMotionless should only be set to MOTIONLESS_FALSE
if some scrolling occurs, even in the case where motion is discarded
by snap-scroll mode.

Refactoring the code allows the code to be smaller, and provides
a single point where scrollBy() is called while dragging.

This doesn't change the snap-scroll logic in any way.

related to http://b/issue?id=2092446

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base