Enable flattening/unflattening with custom unflatten procs

src/core/SkReadBuffer.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmap.h"
 #include "SkErrorInternals.h"
 #include "SkImage.h"
@@ skipping 330 matching lines @@
         if (0 == index) {
             return nullptr; // writer failed to give us the flattenable
         }
         index -= 1;     // we stored the index-base-1
         if ((unsigned)index >= (unsigned)fFactoryCount) {
             this->validate(false);
             return nullptr;
         }
         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
+            }
         }
     }
 
     // if we get here, factory may still be null, but if that is the case, the
     // failure was ours, not the writer.
     sk_sp<SkFlattenable> obj;
     uint32_t sizeRecorded = fReader.readU32();
     if (factory) {
         size_t offset = fReader.offset();
         obj = (*factory)(*this);
@@ skipping 20 matching lines @@
             return;
         }
     } else {
         if (nullptr == this->readFunctionPtr()) {
             return;
         }
     }
     uint32_t sizeRecorded = fReader.readU32();
     fReader.skip(sizeRecorded);
 }