Update V8 to r3121 as required for WebKit update.

Change-Id: Ic53e0aef9a9eb9b71ee7d25a8aef61520bba899c
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index cbd47a8..5a3ab89 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -279,11 +279,9 @@
 
   void VisitDebugTarget(RelocInfo* rinfo) {
     ASSERT(RelocInfo::IsJSReturn(rinfo->rmode()) &&
-           rinfo->IsCallInstruction());
+           rinfo->IsPatchedReturnSequence());
     HeapObject* code = Code::GetCodeFromTargetAddress(rinfo->call_address());
     MarkCompactCollector::MarkObject(code);
-    // When compacting we convert the call to a real object pointer.
-    if (IsCompacting()) rinfo->set_call_object(code);
   }
 
  private:
@@ -1383,6 +1381,15 @@
         reinterpret_cast<Code*>(target)->instruction_start());
   }
 
+  void VisitDebugTarget(RelocInfo* rinfo) {
+    ASSERT(RelocInfo::IsJSReturn(rinfo->rmode()) &&
+           rinfo->IsPatchedReturnSequence());
+    Object* target = Code::GetCodeFromTargetAddress(rinfo->call_address());
+    VisitPointer(&target);
+    rinfo->set_call_address(
+        reinterpret_cast<Code*>(target)->instruction_start());
+  }
+
  private:
   void UpdatePointer(Object** p) {
     if (!(*p)->IsHeapObject()) return;