Solve three memory leaks related to PatchCache

A Patch can be fairly large, holding bitmap data, but
is also frequently leaked which adds to the severity.
The feature is used in many important processes such
as Home, SystemUI and Chrome.

The following leaks are solved:

1. The Patch itself was not always freed.
PatchCache::removeDeferred() can mark patches to be
cared for by PatchCache::clearGarbage(). But
mCache.remove() would only destroy the container
and the pointer, not the Patch object itself.

2. The vertices stored in the Patch at Patch::createMesh()
would always leak. The empty/default destructor in Patch
would not properly destroy "vertices" since it's just a
pointer.

3. A BufferBlock that's added to the mFreeBlocks
in PatchCache could leak. The leak happened when a
patch later needed the entire free block, because the
object was removed from the list but never deleted
in PatchCache::setupMesh().

Change-Id: I41e60824479230b67426fc546d3dbff294c8891f
hwui: Fix a sporadic crash seen during CTS runs

 * It's possible (due to race conditions) that a patch might be
   scheduled for removal twice. Just print a warning and continue
   instead of asserting and crashing.

Change-Id: I42865f6717816a743cc49ba15b839e6c3b57ed83