Clean up Track constructor

The 'thread' parameter can never be NULL.
Use constructor initialization list when possible.
Make more members const.
Only put the relevant code under "if (mCblk != NULL)".
Add comment about track name leak.

Change-Id: Ib963390a69bed1999638cc982a759edd1d5f4712
diff --git a/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index 0e4b24a..b75d3a1 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -681,9 +681,9 @@
             enum {FS_FILLING, FS_FILLED, FS_ACTIVE};
             mutable uint8_t     mFillingUpStatus;
             int8_t              mRetryCount;
-            sp<IMemory>         mSharedBuffer;
+            const sp<IMemory>   mSharedBuffer;
             bool                mResetDone;
-            audio_stream_type_t mStreamType;
+            const audio_stream_type_t mStreamType;
             int                 mName;
             int16_t             *mMainBuffer;
             int32_t             *mAuxBuffer;