Change ConsumerBase's FrameAvailableListener to be a weak pointer

This prevents strong reference cycles when the listener implementation also
holds a strong pointer to the ConsumerBase

Bug: 7425644
Change-Id: I1514b13a32b18d421c902dddebec0765a989c55c
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index 6f75d8c..54099f4 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -47,7 +47,8 @@
 
 // ---------------------------------------------------------------------------
 
-class Layer : public LayerBaseClient
+class Layer : public LayerBaseClient,
+              public SurfaceTexture::FrameAvailableListener
 {
 public:
             Layer(SurfaceFlinger* flinger, const sp<Client>& client);
@@ -102,13 +103,15 @@
 
 private:
     friend class SurfaceTextureLayer;
-    void onFrameQueued();
     virtual sp<ISurface> createSurface();
     uint32_t getEffectiveUsage(uint32_t usage) const;
     bool isCropped() const;
     Rect computeBufferCrop() const;
     static bool getOpacityForFormat(uint32_t format);
 
+    // Interface implementation for SurfaceTexture::FrameAvailableListener
+    virtual void onFrameAvailable();
+
     // -----------------------------------------------------------------------
 
     // constants