Reverts refactoring of CPU feature detection for

runtime/vm/assembler_x64.h

 // Copyright (c) 2013, 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_ASSEMBLER_X64_H_
 #define VM_ASSEMBLER_X64_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_x64.h directly; use assembler.h instead.
 #endif
@@ skipping 299 matching lines @@
 
   intptr_t position_;
   intptr_t unresolved_;
   intptr_t unresolved_near_positions_[kMaxUnresolvedBranches];
 
   friend class Assembler;
   DISALLOW_COPY_AND_ASSIGN(Label);
 };
 
 
+class CPUFeatures : public AllStatic {
+ public:
+  static void InitOnce();
+  // x64 always has at least SSE2.
+  static bool sse2_supported() { return true; }
+  static bool sse4_1_supported();
+  static bool double_truncate_round_supported() { return sse4_1_supported(); }
+
+ private:
+  static const uint64_t kSSE4_1BitMask = static_cast<uint64_t>(1) << 51;
+
+  static bool sse4_1_supported_;
+#ifdef DEBUG
+  static bool initialized_;
+#endif
+};
+
+
 class Assembler : public ValueObject {
  public:
   explicit Assembler(bool use_far_branches = false);
 
   ~Assembler() { }
 
   static const bool kNearJump = true;
   static const bool kFarJump = false;
 
   /*
@@ skipping 729 matching lines @@
 }
 
 
 inline void Assembler::EmitOperandSizeOverride() {
   EmitUint8(0x66);
 }
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_X64_H_