Fix capture overruns at non-primary sample rate

and small buffer size.  Also:
Pull out the magic number "12 ms" to a named constant.
Remove obsolete AudioFlinger::mPrimaryOutputSampleRate.

Bug: 22662814
Change-Id: I261f75a222c4505a84aad2493d251bd2dea59f68
diff --git a/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index 4f7e27d..20c34ef 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -763,9 +763,7 @@
 
     sp<PatchPanel> mPatchPanel;
 
-    uint32_t    mPrimaryOutputSampleRate;   // sample rate of the primary output, or zero if none
-                                            // protected by mHardwareLock
-    bool       mSystemReady;
+    bool        mSystemReady;
 };
 
 #undef INCLUDING_FROM_AUDIOFLINGER_H