Simplify flattening to just write enough to call the factory/public-constructor for the class. We want to *not* rely on private constructors, and not rely on calling through the inheritance hierarchy for either flattening or unflattening(CreateProc).

Refactoring pattern:

1. guard the existing constructor(readbuffer) with the legacy build-flag
2. If you are a instancable subclass, implement CreateProc(readbuffer) to create a new instances from the buffer params (or return NULL).

If you're a shader subclass
1. You must read/write the local matrix if your class accepts that in its factory/constructor, else ignore it.

R=robertphillips@google.com, mtklein@google.com, senorblanco@google.com, senorblanco@chromium.org, sugoi@chromium.org

Author: reed@google.com

Review URL: https://codereview.chromium.org/395603002
diff --git a/samplecode/SampleAll.cpp b/samplecode/SampleAll.cpp
index 92fe258..395314c 100644
--- a/samplecode/SampleAll.cpp
+++ b/samplecode/SampleAll.cpp
@@ -172,9 +172,11 @@
         dst->addCircle(loc.fX, loc.fY, fRadius);
     }
 
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
     Dot2DPathEffect(SkReadBuffer& buffer) : INHERITED(buffer) {
         fRadius = buffer.readScalar();
     }
+#endif
     virtual void flatten(SkWriteBuffer& buffer) const SK_OVERRIDE {
         this->INHERITED::flatten(buffer);
         buffer.writeScalar(fRadius);