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/src/effects/SkAvoidXfermode.cpp b/src/effects/SkAvoidXfermode.cpp
index ffe6a21..aae6ba5 100644
--- a/src/effects/SkAvoidXfermode.cpp
+++ b/src/effects/SkAvoidXfermode.cpp
@@ -15,24 +15,30 @@
     if (tolerance > 255) {
         tolerance = 255;
     }
-
+    fTolerance = SkToU8(tolerance);
     fOpColor = opColor;
     fDistMul = (256 << 14) / (tolerance + 1);
     fMode = mode;
 }
 
-SkAvoidXfermode::SkAvoidXfermode(SkReadBuffer& buffer)
-    : INHERITED(buffer) {
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
+SkAvoidXfermode::SkAvoidXfermode(SkReadBuffer& buffer) : INHERITED(buffer) {
     fOpColor = buffer.readColor();
     fDistMul = buffer.readUInt();
     fMode = (Mode)buffer.readUInt();
 }
+#endif
+
+SkFlattenable* SkAvoidXfermode::CreateProc(SkReadBuffer& buffer) {
+    const SkColor color = buffer.readColor();
+    const unsigned tolerance = buffer.readUInt();
+    const unsigned mode = buffer.readUInt();
+    return Create(color, tolerance, (Mode)mode);
+}
 
 void SkAvoidXfermode::flatten(SkWriteBuffer& buffer) const {
-    this->INHERITED::flatten(buffer);
-
     buffer.writeColor(fOpColor);
-    buffer.writeUInt(fDistMul);
+    buffer.writeUInt(fTolerance);
     buffer.writeUInt(fMode);
 }