[ActivityManager] Reduce report ANR on wrong activity.

Symptom: ANR report on wrong activity.

Root Cause:
  KK changed resume behavior that will not update focus when only resume,
if the activity blocked, it may report ANR on previous focus.
  By original concept, it will try to correct the ANR target,
but the stack of waiting(waitingVisible=true) activity may
different with current top stack.
  If it gets key dispatch timeout, mResumedActivity and mPausingActivity
of its stack will be null becuase it is not top stack.
Then it is unable to change ANR target to the real no response activity.

Solution:
 Use focused stack to get the real culprit.

Reproduce steps:
1.Launch an Activity X from launcher, press home key.
2.Launch X from launcher again, X blocks(sleeps 15sec) in onResume, press back key in the beginning of blocking duration.
3.ANR dialog shows launcher is no response.

Change-Id: I99416ad91e349096f995990f2240a97616fbaf28
Don't allow MemoryFiles of negative length.

Prevents us from converting a (signed) jint into an
(unsigned) size_t and having horrible things happen.

Change-Id: I0f04e2eb9852ae7fc49b435fd0974f56e86751a4
ConnectivtyService : Execute connectivityCheck in thread pool

Since this async task takes long when doing things like waiting for
network connectivity...etc, rather than holding up the single executor
of async task for the framework (app_process), run it on a thread from
the pool so other tasks can execute in parallel.

Change-Id: I7b88a4837c7e117ef47014a20c57f828b811edfb