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/tests/GLProgramsTest.cpp b/tests/GLProgramsTest.cpp
index 9da1ecc..5763211 100644
--- a/tests/GLProgramsTest.cpp
+++ b/tests/GLProgramsTest.cpp
@@ -274,7 +274,7 @@
 void forceLinking() {
     SkLightingImageFilter::CreateDistantLitDiffuse(SkPoint3(0,0,0), 0, 0, 0);
     SkAlphaThresholdFilter::Create(SkRegion(), .5f, .5f);
-    SkAutoTUnref<SkMagnifierImageFilter> mag(SkMagnifierImageFilter::Create(
+    SkAutoTUnref<SkImageFilter> mag(SkMagnifierImageFilter::Create(
         SkRect::MakeWH(SK_Scalar1, SK_Scalar1), SK_Scalar1));
     GrConfigConversionEffect::Create(NULL,
                                      false,