audioflinger: add HOTWORD audio source.

HOTWORD is a special capture audio source that uses
the same audio tuning as VOICE_RECOGNITION but allows an
active capture to be preempted.

Bug: 10640877.

Change-Id: Iea09a11cbcdbacc8d434e5230e7559dcd1b44ac0
diff --git a/services/audioflinger/Threads.cpp b/services/audioflinger/Threads.cpp
index e35f47e..1b5a9a9 100644
--- a/services/audioflinger/Threads.cpp
+++ b/services/audioflinger/Threads.cpp
@@ -4451,6 +4451,10 @@
 
     {
         Mutex::Autolock _l(mLock);
+        for (size_t i = 0; i < mTracks.size(); i++) {
+            sp<RecordTrack> track = mTracks[i];
+            track->invalidate();
+        }
         mActiveTrack.clear();
         mStartStopCond.broadcast();
     }