This has a good, although small, impact on performance : it removes
a two-way IPC call in a most frequent case, while possibly adding
one in a rather unfrequent and less critical case.

Also, this fixes a bug with surrogate pairs. This specific branch
of code now correctly handles surrogate pairs.
Aside from this, it should have no impact on behavior.

However, since it does delay access to the previous character in
the text view by a two-way IPC call, it actually goes a long way
toward fixing bug#6668226. It is not really a fix and the race
condition still exists, but this change makes it much, much
harder to hit.

Bug: 6668226
Change-Id: Id11cc6a0b7488d6bd392227cafdcf3a8d4c62f6c

This is harmless, but against policy.
Also, rework the checking code to be more readable, give more
information, and be called for all relevant methods - and not
for informative methods, which are not required to be in a
batch edit.

Change-Id: I03fa8b2e7d68a6a133f86be8a214671750c29256

Change-Id: I512b04e23490413a44b1ca0517102fe2d9138df3

Change-Id: Ie143ad008ca8deb1c5034cb80ec1cb28a6b0682d

Change-Id: If8d03bea1b6369cb3043da6321048d052995d664

Change-Id: I8527776a4bd8236a85bb77f9791f9b76977ad181

Change-Id: I9982ff325bef56694402caef28a77683c52ccd71

The goal is to simplify the code in LatinIME.java as well as having
a handy place to put debug calls to see interaction with TextView.

Change-Id: I255227e7e7343e0c2f3dcd1f185e5020d6186732