Use audio_io_handle_t consistently instead of int

Other:
 - add a comment to nextUniqueId
 - made ThreadBase::mId const, since it is only assigned in constructor.

Change-Id: I4e8b7bec4e45badcde6274d574b8a9aabd046837
diff --git a/include/media/IAudioFlingerClient.h b/include/media/IAudioFlingerClient.h
index aa0cdcf..f3b4df1 100644
--- a/include/media/IAudioFlingerClient.h
+++ b/include/media/IAudioFlingerClient.h
@@ -21,6 +21,7 @@
 #include <utils/RefBase.h>
 #include <binder/IInterface.h>
 #include <utils/KeyedVector.h>
+#include <system/audio.h>
 
 namespace android {
 
@@ -32,7 +33,7 @@
     DECLARE_META_INTERFACE(AudioFlingerClient);
 
     // Notifies a change of audio input/output configuration.
-    virtual void ioConfigChanged(int event, int ioHandle, void *param2) = 0;
+    virtual void ioConfigChanged(int event, audio_io_handle_t ioHandle, void *param2) = 0;
 
 };