[webkit] Runtime enablement of WebGL

Hook up debug setting to enable/disable WebGL.

(cherry-picked from commit 69ee15e5b0bc1e0b2d41d80f9f5247b826c62ceb)

Change-Id: Ib07427378450a858d6b6308e23b5e1aaac002dd3
[webkit]Change the thread priority

Change the values used to dynamically modify thread priority to
improve scrolling and pinc to zoom use cases.

Change-Id: I861b3042079058fdd614390c563f23d3cab3acd9
[webkit] Postpone sending scroll message to webcore thread

Post a message to the UI thread instead, to send the
scroll message later. Thus reduce the computation until
currnet scrolling finishes

Change-Id: Iff94af37e9070e63e0797195c7588343ab077bb3
frameworks/base: Fix to avoid crash when the tab is not set from app

As the current tab is not set from application, getChildTabViewAt
returns Null value. Added a condition which checks whether mSelectTab
is set to first Tab.

(cherry picked from commit 9be6755efb149b22c36aa3eb7cc4ffe7e765e08a)

Change-Id: I11c77ca96333e2663d28db1b5fdb46602bd9e745
CRs-Fixed: 321176