Add PushAddress(ExternalReference) for X64.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 6bb5cfeb429a2f3f2fb14964af9d918e97f0eeed..66587d5319a1dffb8fb53a044a5eb9f2b46c2285 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -127,6 +127,8 @@ class MacroAssembler: public Assembler {
   // Returns the size of the code generated by LoadAddress.
   // Used by CallSize(ExternalReference) to find the size of a call.
   int LoadAddressSize(ExternalReference source);
+  // Pushes the address of the external reference onto the stack.
+  void PushAddress(ExternalReference source);
 
   // Operations on roots in the root-array.
   void LoadRoot(Register destination, Heap::RootListIndex index);