Enable flattening/unflattening with custom unflatten procs

src/core/SkReadBuffer.cpp

Index: src/core/SkReadBuffer.cpp
diff --git a/src/core/SkReadBuffer.cpp b/src/core/SkReadBuffer.cpp
index f220b5a9e61581b35772b5514c1c6fd307e56d8d..c7bda21a4b159cf790eb74a78a2f145c3fec5df1 100644
--- a/src/core/SkReadBuffer.cpp
+++ b/src/core/SkReadBuffer.cpp
@@ -348,9 +348,16 @@ SkFlattenable* SkReadBuffer::readFlattenable(SkFlattenable::Type ft) {
         }
         factory = fFactoryArray[index];
     } else {
-        factory = (SkFlattenable::Factory)readFunctionPtr();
-        if (nullptr == factory) {
-            return nullptr; // writer failed to give us the flattenable
+        SkString name;
+        this->readString(&name);
+
+        // Check if a custom Factory has been specified for this flattenable.

[reed1, 2016/04/11 15:07:48]

Is this order (checking custom first) important? Do we need to document that in
the header?

[msarett, 2016/04/19 18:03:50]

Yes I think we should check custom first.  I've this to the header.

+        factory = getCustomFactory(name.c_str());
+        if (!factory) {
+            factory = SkFlattenable::NameToFactory(name.c_str());
+            if (!factory) {
+                return nullptr; // writer failed to give us the flattenable
+            }
         }
     }