X64: Implement debugger hooks.

src/ia32/assembler-ia32.h

Index: src/ia32/assembler-ia32.h
diff --git a/src/ia32/assembler-ia32.h b/src/ia32/assembler-ia32.h
index b648055f1b9addecf6c7f3c2fe234d9b726682ac..5203a66bb01ac6208ace7d7dc98f1a16e2efaf68 100644
--- a/src/ia32/assembler-ia32.h
+++ b/src/ia32/assembler-ia32.h
@@ -438,6 +438,9 @@ class Assembler : public Malloced {
   // Distance between the address of the code target in the call instruction
   // and the return address
   static const int kTargetAddrToReturnAddrDist = kPointerSize;
+  // Distance between start of patched return sequence and the emitted address
+  // to jump to.
+  static const int kReturnAddrPatchPrefixSize = 1;  // JMP imm32.
 
 
   // ---------------------------------------------------------------------------