Camera2: Move preview callback processing to its own thread.

To reduce delays for HAL callbacks, manage preview callbacks in their
own thread.

Bug: 6243944
Change-Id: I7bef56949ac889ffce4e031bf40291a771a46f3e
diff --git a/services/camera/libcameraservice/Android.mk b/services/camera/libcameraservice/Android.mk
index 9898a70..1370c62 100644
--- a/services/camera/libcameraservice/Android.mk
+++ b/services/camera/libcameraservice/Android.mk
@@ -14,7 +14,8 @@
     camera2/CameraMetadata.cpp \
     camera2/Parameters.cpp \
     camera2/FrameProcessor.cpp \
-    camera2/CaptureProcessor.cpp
+    camera2/CaptureProcessor.cpp \
+    camera2/CallbackProcessor.cpp
 
 LOCAL_SHARED_LIBRARIES:= \
     libui \