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/src/effects/SkEmbossMaskFilter.cpp b/src/effects/SkEmbossMaskFilter.cpp
index 26a5e2e..245ccd6 100644
--- a/src/effects/SkEmbossMaskFilter.cpp
+++ b/src/effects/SkEmbossMaskFilter.cpp
@@ -122,11 +122,12 @@
     fBlurRadius = buffer.readScalar();
 }
 
-void SkEmbossMaskFilter::flatten(SkFlattenableWriteBuffer& buffer) {
+void SkEmbossMaskFilter::flatten(SkFlattenableWriteBuffer& buffer) const {
     this->INHERITED::flatten(buffer);
 
-    fLight.fPad = 0;    // for the font-cache lookup to be clean
-    buffer.writeMul4(&fLight, sizeof(fLight));
+    Light tmpLight = fLight;
+    tmpLight.fPad = 0;    // for the font-cache lookup to be clean
+    buffer.writeMul4(&tmpLight, sizeof(tmpLight));
     buffer.writeScalar(fBlurRadius);
 }