DO NOT MERGE.

Couple of tweak for multi-touch in WebView.

1. If we can't zoom, don't get in multitouch mode.
   This avoid the logo in google.com looks fuzzy.
2. Reset mAnchor after sending VIEW_SIZE_CHANGED.
3. Don't call zoom when finishing multitouch unless
   zoom is called before.
4. Change the width for nativeSetSize, which was modified
   in the last check-in. The new logic should make both
   msn.com and news.google.com looks correct.
5. Use the pressure instead of distance/time to filter
   out the jitter just before lifting the finger.

Fix http://b/issue?id=2360032