AudioPolicyManager: Convert dump to use String8 (part 2)

Test: dumpsys of APM, diffs.
Bug: 117333182
Change-Id: I18761416ec9dc97418b41054f85af67e6eb59f3a
diff --git a/services/audiopolicy/managerdefault/AudioPolicyManager.h b/services/audiopolicy/managerdefault/AudioPolicyManager.h
index fcb9d25..f559b7f 100644
--- a/services/audiopolicy/managerdefault/AudioPolicyManager.h
+++ b/services/audiopolicy/managerdefault/AudioPolicyManager.h
@@ -186,7 +186,9 @@
 
         virtual bool isSourceActive(audio_source_t source) const;
 
-        virtual status_t dump(int fd);
+        void dump(String8 *dst) const; // helper for dump(int fd)
+
+        status_t dump(int fd) override;
 
         virtual bool isOffloadSupported(const audio_offload_info_t& offloadInfo);