Make Flattenable not virtual

Fallout from the Flattenable change, update all its uses.

Additionnaly, fix/tighten size checks when (un)flatten()ing
things.

Removed the assumption by some flattenables (e.g.: Fence)
that the size passed to them would be exact (it can
and will be larger in some cases)

The code in Parcel is a bit complicated so that we don't
have to expose the full implementation (and also to
keep the code smallish).

Change-Id: I0bf1c8aca2a3128491b4f45510bc46667e566dde
diff --git a/include/ui/Region.h b/include/ui/Region.h
index ce91f3b..d906dbb 100644
--- a/include/ui/Region.h
+++ b/include/ui/Region.h
@@ -136,8 +136,8 @@
             void        addRectUnchecked(int l, int t, int r, int b);
 
     inline  bool        isFixedSize() const { return false; }
-            size_t      getSize() const;
-            status_t    flatten(void* buffer) const;
+            size_t      getFlattenedSize() const;
+            status_t    flatten(void* buffer, size_t size) const;
             status_t    unflatten(void const* buffer, size_t size);
 
     void        dump(String8& out, const char* what, uint32_t flags=0) const;