Add support for serializing/deserializing of SkDrawable

src/core/SkReadBuffer.cpp

Index: src/core/SkReadBuffer.cpp
diff --git a/src/core/SkReadBuffer.cpp b/src/core/SkReadBuffer.cpp
index 2dd9f093ac2be7e21da632f84e7f03cc15bbc0c7..cc591c7258b7922b99418fdacf8fe0d144023688 100644
--- a/src/core/SkReadBuffer.cpp
+++ b/src/core/SkReadBuffer.cpp
@@ -33,6 +33,7 @@ SkReadBuffer::SkReadBuffer() {
 
     fFactoryArray = nullptr;
     fFactoryCount = 0;
+    fCustomFactory.reset(new SkTHashMap<SkFlattenable::Factory, SkFlattenable::Factory>());
     fBitmapDecoder = nullptr;
 #ifdef DEBUG_NON_DETERMINISTIC_ASSERT
     fDecodedBitmapIndex = -1;
@@ -51,6 +52,7 @@ SkReadBuffer::SkReadBuffer(const void* data, size_t size) {
 
     fFactoryArray = nullptr;
     fFactoryCount = 0;
+    fCustomFactory.reset(new SkTHashMap<SkFlattenable::Factory, SkFlattenable::Factory>());
     fBitmapDecoder = nullptr;
 #ifdef DEBUG_NON_DETERMINISTIC_ASSERT
     fDecodedBitmapIndex = -1;
@@ -71,6 +73,7 @@ SkReadBuffer::SkReadBuffer(SkStream* stream) {
 
     fFactoryArray = nullptr;
     fFactoryCount = 0;
+    fCustomFactory.reset(new SkTHashMap<SkFlattenable::Factory, SkFlattenable::Factory>());
     fBitmapDecoder = nullptr;
 #ifdef DEBUG_NON_DETERMINISTIC_ASSERT
     fDecodedBitmapIndex = -1;
@@ -352,6 +355,12 @@ SkFlattenable* SkReadBuffer::readFlattenable(SkFlattenable::Type ft) {
         if (nullptr == factory) {
             return nullptr; // writer failed to give us the flattenable
         }
+
+        // Check if a custom Factory has been specified for this flattenable.
+        SkFlattenable::Factory* customFactoryPtr = getCustomFactory(factory);
+        if (customFactoryPtr) {
+            factory = *customFactoryPtr;
+        }
     }
 
     // if we get here, factory may still be null, but if that is the case, the