Shorter TryAllocate instruction sequence on ARM/ARM64/MIPS.

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 752 matching lines @@
 
   void SmiUntag(Register reg) {
     sarq(reg, Immediate(kSmiTagSize));
   }
 
   int PreferredLoopAlignment() { return 16; }
   void Align(int alignment, intptr_t offset);
   void Bind(Label* label);
 
   void Comment(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
+  static bool EmittingComments();
+
   const Code::Comments& GetCodeComments() const;
 
   intptr_t CodeSize() const { return buffer_.Size(); }
   intptr_t prologue_offset() const { return prologue_offset_; }
 
   // Count the fixups that produce a pointer offset, without processing
   // the fixups.
   intptr_t CountPointerOffsets() const {
     return buffer_.CountPointerOffsets();
   }
@@ skipping 312 matching lines @@
 }
 
 
 inline void Assembler::EmitOperandSizeOverride() {
   EmitUint8(0x66);
 }
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_X64_H_