Make some constants' meaning clear for X64

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 13d7ddaa685bf92e16a4adab1faa1dc17fee4aae..8f430bc23d3b970b0278da8849f26f632fb9e47f 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -155,7 +155,7 @@ int MacroAssembler::LoadAddressSize(ExternalReference source) {
     }
   }
   // Size of movq(destination, src);
-  return 10;
+  return Assembler::kMoveAddressIntoScratchRegisterInstructionLength;
 }
 
 
@@ -2510,8 +2510,8 @@ void MacroAssembler::Jump(Handle<Code> code_object, RelocInfo::Mode rmode) {
 
 int MacroAssembler::CallSize(ExternalReference ext) {
   // Opcode for call kScratchRegister is: Rex.B FF D4 (three bytes).
-  const int kCallInstructionSize = 3;
-  return LoadAddressSize(ext) + kCallInstructionSize;
+  return LoadAddressSize(ext) +
+         Assembler::kCallScratchRegisterInstructionLength;
 }