Cache lookups at megamorphic call sites in optimized code.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index 0b305adcdf51e36574cc74bfb0ec9fc7d8d60b4a..b9412df9537d50906c112613b5d619d15c3c483c 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -40,6 +40,7 @@ namespace dart {
   V(Context)                                                                   \
   V(ContextScope)                                                              \
   V(ICData)                                                                    \
+  V(MegamorphicCache)                                                          \
   V(SubtypeTestCache)                                                          \
   V(Error)                                                                     \
     V(ApiError)                                                                \
@@ -934,6 +935,22 @@ class RawICData : public RawObject {
 };
 
 
+class RawMegamorphicCache : public RawObject {
+  RAW_HEAP_OBJECT_IMPLEMENTATION(MegamorphicCache);
+
+  RawObject** from() {
+    return reinterpret_cast<RawObject**>(&ptr()->buckets_);
+  }
+  RawArray* buckets_;
+  RawSmi* mask_;
+  RawObject** to() {
+    return reinterpret_cast<RawObject**>(&ptr()->mask_);
+  }
+
+  intptr_t fill_count_;
+};
+
+
 class RawSubtypeTestCache : public RawObject {
   RAW_HEAP_OBJECT_IMPLEMENTATION(SubtypeTestCache);
   RawArray* cache_;