X64: Implement debugger hooks.

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
diff --git a/src/x64/assembler-x64.h b/src/x64/assembler-x64.h
index 2130fb0379c245e2c78185ae4999648d67bf4472..a5eb775a48c4e90d30432b7dd2abbbfba91d7f2f 100644
--- a/src/x64/assembler-x64.h
+++ b/src/x64/assembler-x64.h
@@ -443,7 +443,9 @@ class Assembler : public Malloced {
   // Distance between the address of the code target in the call instruction
   // and the return address.  Checked in the debug build.
   static const int kTargetAddrToReturnAddrDist = 3 + kPointerSize;
-
+  // Distance between start of patched return sequence and the emitted address
+  // to jump to.
+  static const int kReturnAddrPatchPrefixSize = 2;  // movq = REX.W 0xB8+r.
 
   // ---------------------------------------------------------------------------
   // Code generation
@@ -917,6 +919,9 @@ class Assembler : public Malloced {
   // Jump near absolute indirect (r64)
   void jmp(Register adr);
 
+  // Jump near absolute indirect (m64)
+  void jmp(const Operand& src);
+
   // Conditional jumps
   void j(Condition cc, Label* L);