Using centralized isAudioPlaybackRateValid to validate parameters

Centralized validation code
bug: 20701446

Change-Id: I9d9941c7639c05b2afe069ff4f858c693c910bfe
diff --git a/services/audioflinger/BufferProviders.h b/services/audioflinger/BufferProviders.h
index 4970b6c..4bc895c 100644
--- a/services/audioflinger/BufferProviders.h
+++ b/services/audioflinger/BufferProviders.h
@@ -188,6 +188,7 @@
     sonicStream          mSonicStream;            // handle to sonic timestretch object
     //FIXME: this dependency should be abstracted out
     bool                 mFallbackFailErrorShown; // log fallback error only once
+    bool                 mAudioPlaybackRateValid; // flag for current parameters validity
 };
 
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