Cleanup code related to SkFlattenable::flatten()

The following changes were made by this CL:

1. Make flatten() a protected method as callers should use
   SkFlattenableWriteBuffer to flatten an object
2. Make flatten a const method (including subclasses)
3. Mark subclass implementation of flatten with SK_OVERRIDE
4. Ensure overridden flatten impls call their parent
5. Remove no-op implementations of flatten from subclasses

Additionally, if necessary the unflattening constructor was
also moved to the protected section of the subclasses
header if it was not already there.

git-svn-id: http://skia.googlecode.com/svn/trunk@3540 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/samplecode/SampleTextEffects.cpp b/samplecode/SampleTextEffects.cpp
index e6bca82..a37d103 100644
--- a/samplecode/SampleTextEffects.cpp
+++ b/samplecode/SampleTextEffects.cpp
@@ -189,10 +189,6 @@
         return false;
     }
 
-    virtual void flatten(SkFlattenableWriteBuffer& buffer) {
-        this->INHERITED::flatten(buffer);
-        buffer.writeScalar(fWidth);
-    }
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(Line2DPathEffect)
 
 protected:
@@ -211,9 +207,13 @@
         }
     }
 
-    Line2DPathEffect(SkFlattenableReadBuffer& buffer) : Sk2DPathEffect(buffer) {
+    Line2DPathEffect(SkFlattenableReadBuffer& buffer) : INHERITED(buffer) {
         fWidth = buffer.readScalar();
     }
+    virtual void flatten(SkFlattenableWriteBuffer& buffer) const SK_OVERRIDE {
+        this->INHERITED::flatten(buffer);
+        buffer.writeScalar(fWidth);
+    }
 
 private:
     SkScalar fWidth;