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

vm/instructions_x64_test.cc

 // Copyright (c) 2012, 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/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/instructions.h"
 #include "vm/stub_code.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
 #define __ assembler->
 
 ASSEMBLER_TEST_GENERATE(Call, assembler) {
-  __ call(&StubCode::MegamorphicLookupLabel());
+  __ call(&StubCode::InstanceFunctionLookupLabel());
   __ ret();
 }
 
 
 ASSEMBLER_TEST_RUN(Call, entry) {
   CallPattern call(entry);
-  EXPECT_EQ(StubCode::MegamorphicLookupLabel().address(), call.TargetAddress());
+  EXPECT_EQ(StubCode::InstanceFunctionLookupLabel().address(),
+            call.TargetAddress());
 }
 
 
 ASSEMBLER_TEST_GENERATE(Jump, assembler) {
-  __ jmp(&StubCode::MegamorphicLookupLabel());
+  __ jmp(&StubCode::InstanceFunctionLookupLabel());
   __ jmp(&StubCode::AllocateArrayLabel());
   __ ret();
 }
 
 
 ASSEMBLER_TEST_RUN(Jump, entry) {
   JumpPattern jump1(entry);
   jump1.IsValid();
-  EXPECT_EQ(StubCode::MegamorphicLookupLabel().address(),
+  EXPECT_EQ(StubCode::InstanceFunctionLookupLabel().address(),
             jump1.TargetAddress());
   JumpPattern jump2(entry + jump1.pattern_length_in_bytes());
   EXPECT_EQ(StubCode::AllocateArrayLabel().address(),
             jump2.TargetAddress());
   uword target1 = jump1.TargetAddress();
   uword target2 = jump2.TargetAddress();
   jump1.SetTargetAddress(target2);
   jump2.SetTargetAddress(target1);
   EXPECT_EQ(StubCode::AllocateArrayLabel().address(),
             jump1.TargetAddress());
-  EXPECT_EQ(StubCode::MegamorphicLookupLabel().address(),
+  EXPECT_EQ(StubCode::InstanceFunctionLookupLabel().address(),
             jump2.TargetAddress());
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64