Reapply "Improve hashCode for closure objects" with fixes.

runtime/vm/precompiler.cc

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/precompiler.h"
 
 #include "vm/aot_optimizer.h"
 #include "vm/assembler.h"
 #include "vm/ast_printer.h"
 #include "vm/branch_optimizer.h"
@@ skipping 618 matching lines @@
         (cid == kFreeListElement) || (cid == kForwardingCorpse)) {
       continue;
     }
     cls = isolate()->class_table()->At(cid);
     AddInstantiatedClass(cls);
   }
 
   Dart_QualifiedFunctionName vm_entry_points[] = {
     // Functions
     {"dart:core", "::", "_completeDeferredLoads"},
+    {"dart:core", "::", "identityHashCode"},
     {"dart:core", "AbstractClassInstantiationError",
      "AbstractClassInstantiationError._create"},
     {"dart:core", "ArgumentError", "ArgumentError."},
     {"dart:core", "ArgumentError", "ArgumentError.value"},
     {"dart:core", "CyclicInitializationError", "CyclicInitializationError."},
     {"dart:core", "FallThroughError", "FallThroughError._create"},
     {"dart:core", "FormatException", "FormatException."},
     {"dart:core", "NoSuchMethodError", "NoSuchMethodError._withType"},
     {"dart:core", "NullThrownError", "NullThrownError."},
     {"dart:core", "OutOfMemoryError", "OutOfMemoryError."},
@@ skipping 2676 matching lines @@
 
   ASSERT(FLAG_precompiled_mode);
   const bool optimized = function.IsOptimizable();  // False for natives.
   DartPrecompilationPipeline pipeline(zone, field_type_map);
   return PrecompileFunctionHelper(precompiler, &pipeline, function, optimized);
 }
 
 #endif  // DART_PRECOMPILER
 
 }  // namespace dart