Serializer: cache hashmaps on the isolate.

src/snapshot-source-sink.cc

Index: src/snapshot-source-sink.cc
diff --git a/src/snapshot-source-sink.cc b/src/snapshot-source-sink.cc
index 0054aec27c154afd795199361ef28a2d24e2a51c..eedcee6a9cebc52beea08338e7f9152eafd0b6c1 100644
--- a/src/snapshot-source-sink.cc
+++ b/src/snapshot-source-sink.cc
@@ -14,7 +14,7 @@ namespace v8 {
 namespace internal {
 
 void SnapshotByteSource::CopyRaw(byte* to, int number_of_bytes) {
-  MemCopy(to, data_ + position_, number_of_bytes);
+  memcpy(to, data_ + position_, number_of_bytes);
   position_ += number_of_bytes;
 }