Dynamically configure the number of video buffers used by camera source, if supported

o related-to-bug: 6920805

Change-Id: I413bb50954cc84e32ed40bcb713842dc7b58e2b6
diff --git a/services/camera/libcameraservice/Camera2Client.h b/services/camera/libcameraservice/Camera2Client.h
index 8ae16a4..9bea8f1 100644
--- a/services/camera/libcameraservice/Camera2Client.h
+++ b/services/camera/libcameraservice/Camera2Client.h
@@ -288,7 +288,8 @@
     // TODO: This needs to be queried from somewhere, or the BufferQueue needs
     // to be passed all the way to stagefright. Right now, set to a large number
     // to avoid starvation of the video encoders.
-    static const size_t kRecordingHeapCount = 8;
+    static const size_t kDefaultRecordingHeapCount = 8;
+    size_t mRecordingHeapCount;
     size_t mRecordingHeapHead, mRecordingHeapFree;
     // Handle new recording image buffers
     void onRecordingFrameAvailable();