Remove functions_cache_ and it's references as it is not being used anymore.

vm/stub_code.h

 // Copyright (c) 2011, 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.
 
 #ifndef VM_STUB_CODE_H_
 #define VM_STUB_CODE_H_
 
 #include "vm/allocation.h"
 #include "vm/assembler.h"
 
 namespace dart {
 
 // Forward declarations.
 class Code;
 class Isolate;
 class ObjectPointerVisitor;
 class RawCode;
 
 
 // List of stubs created in the VM isolate, these stubs are shared by different
 // isolates running in this dart process.
 #define VM_STUB_CODE_LIST(V)                                                   \
   V(CallToRuntime)                                                             \
   V(PrintStopMessage)                                                          \
   V(CallNativeCFunction)                                                       \
   V(AllocateArray)                                                             \
   V(CallNoSuchMethodFunction)                                                  \
-  V(MegamorphicLookup)                                                         \
+  V(InstanceFunctionLookup)                                                    \
   V(CallStaticFunction)                                                        \
   V(CallClosureFunction)                                                       \
   V(FixCallersTarget)                                                          \
   V(Deoptimize)                                                                \
   V(BreakpointStatic)                                                          \
   V(BreakpointReturn)                                                          \
   V(Subtype1TestCache)                                                         \
   V(Subtype2TestCache)                                                         \
   V(Subtype3TestCache)                                                         \
   V(GetStackPointer)                                                           \
@@ skipping 140 matching lines @@
                                              const Class& cls);
   static void GenerateAllocationStubForClosure(Assembler* assembler,
                                                const Function& func);
   static void GenerateNArgsCheckInlineCacheStub(Assembler* assembler,
                                                 intptr_t num_args);
 };
 
 }  // namespace dart
 
 #endif  // VM_STUB_CODE_H_