Omits size bits when writing RawObject tags to a snapshot.

runtime/vm/snapshot.h

Index: runtime/vm/snapshot.h
===================================================================
--- runtime/vm/snapshot.h	(revision 37600)
+++ runtime/vm/snapshot.h	(working copy)
@@ -196,6 +196,11 @@
     return result;
   }
 
+  intptr_t ReadTags() {
+    const intptr_t tags = static_cast<intptr_t>(Read<int8_t>()) & 0xff;
+    ASSERT(SerializedHeaderTag::decode(tags) != kObjectId);
+    return tags;
+  }
 
   const uint8_t* CurrentBufferAddress() const {
     return stream_.AddressOfCurrentPosition();
@@ -440,6 +445,12 @@
     WriteIntptrValue(value);
   }
 
+  void WriteTags(intptr_t tags) {
+    ASSERT(SerializedHeaderTag::decode(tags) != kObjectId);
+    const intptr_t flags = tags & 0xff;
+    Write<int8_t>(static_cast<int8_t>(flags));
+  }
+
   // Write out a buffer of bytes.
   void WriteBytes(const uint8_t* addr, intptr_t len) {
     stream_.WriteBytes(addr, len);