Add VM class for Map/LinkedHashMap.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
===================================================================
--- runtime/vm/raw_object.h	(revision 38576)
+++ runtime/vm/raw_object.h	(working copy)
@@ -72,6 +72,7 @@
     V(JSRegExp)                                                                \
     V(WeakProperty)                                                            \
     V(MirrorReference)                                                         \
+    V(LinkedHashMap)                                                         \
     V(UserTag)                                                                 \
 
 #define CLASS_LIST_ARRAYS(V)                                                   \
@@ -1498,6 +1499,7 @@
   friend class RawImmutableArray;
   friend class SnapshotReader;
   friend class GrowableObjectArray;
+  friend class LinkedHashMap;
   friend class Object;
   friend class ICData;  // For high performance access.
   friend class SubtypeTestCache;  // For high performance access.
@@ -1528,6 +1530,23 @@
 };
 
 
+class RawLinkedHashMap : public RawInstance {
+  RAW_HEAP_OBJECT_IMPLEMENTATION(LinkedHashMap);
+
+  RawObject** from() {
+    return reinterpret_cast<RawObject**>(&ptr()->type_arguments_);
+  }
+  RawTypeArguments* type_arguments_;
+  RawInstance* cme_mark_;
+  RawArray* data_;
+  RawObject** to() {
+    return reinterpret_cast<RawObject**>(&ptr()->data_);
+  }
+
+  friend class SnapshotReader;
+};
+
+
 class RawFloat32x4 : public RawInstance {
   RAW_HEAP_OBJECT_IMPLEMENTATION(Float32x4);