X64: Implement debugger hooks.

src/arm/assembler-arm.h

Index: src/arm/assembler-arm.h
diff --git a/src/arm/assembler-arm.h b/src/arm/assembler-arm.h
index eeab4a72cc9e5e139b27177a98fb3de23b660fdf..f6997595bee0d838955a0dd0e0fbe76e37def787 100644
--- a/src/arm/assembler-arm.h
+++ b/src/arm/assembler-arm.h
@@ -431,6 +431,9 @@ class Assembler : public Malloced {
   // Distance between the instruction referring to the address of the call
   // target (ldr pc, [target addr in const pool]) and the return address
   static const int kTargetAddrToReturnAddrDist = sizeof(Instr);
+  // Distance between start of patched return sequence and the emitted address
+  // to jump to.
+  static const int kReturnAddrPatchPrefixSize = 1;
 
 
   // ---------------------------------------------------------------------------