[3171580] Fix two typos related to fixed-size buffers

mFixedSize was never set, this bug was introduced during some "cleanup", in
practice this could cause some issues when a fixed-size buffer was used and
the window was resized.

Layer::drawForSreenShot() had a typo that had no effect.

mFixedSize was used to determine if filtering was needed, which was a bit too
conservative and created a dependency between filtering and "fixed size" states
which should exist.

Now we enable filtering based on the size of the buffer vs. the size of the layer.

Change-Id: I32044e91b0c944c1b137efdceb3f01dfaa78119d
diff --git a/services/surfaceflinger/LayerBase.h b/services/surfaceflinger/LayerBase.h
index d688f65..633df96 100644
--- a/services/surfaceflinger/LayerBase.h
+++ b/services/surfaceflinger/LayerBase.h
@@ -185,7 +185,9 @@
     /**
      * needsLinearFiltering - true if this surface needs filtering
      */
-    virtual bool needsFiltering() const { return mNeedsFiltering; }
+    virtual bool needsFiltering() const {
+        return (!(mFlags & DisplayHardware::SLOW_CONFIG)) && mNeedsFiltering;
+    }
 
     /**
      * isSecure - true if this surface is secure, that is if it prevents