Extend SwipeHelper to support vertical gestures

* Un-hardcode CONSTRAIN_SWIPE and FADE_OUT_DURING_SWIPE, define
  through proper callback, per-layout
* Up (GESTURE_NEGATIVE) and down (GESTURE_POSITIVE), mostly needed
  by new Hover hide /w swipe up gesture

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>
Change-Id: I68c42a8ccabca73a1b241ba7cf264db9c912fccd
HOVER: Implement hide only on swipe up

* Add an Y axis HideHelper, just extend current X axis SwipeHelper and
  change interested methods behaviors
* Some clean up and indenting

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>
Change-Id: I42a260ea993c614b0b9b4558a95dd44dd517c4f1
Remove unnecessary explicit GC in ZygoteInit.

Removes > 1s of GC time and hundreds of GC during device boot.

Zygote size before: 8388608
Zygote size after: 8388608

No increase in zygote space size due to zygote compaction.

Bug: 16398684

Change-Id: I3c6f5a0b26a207ab39bb0a952400d7488e42f00c
Signed-off-by: anerikg <anerikgames@gmail.com>

Conflicts:
	core/java/com/android/internal/os/ZygoteInit.java