[turbofan] escape analysis: support MapGuard node

Bug: v8:6731
Change-Id: I6b07ac90a7d86d0ff915b1e89238df5af6b07926
Reviewed-on: https://chromium-review.googlesource.com/620648Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47462}

src/compiler/new-escape-analysis.cc

@@ -645,6 +645,14 @@ void ReduceNode(const Operator* op, EscapeAnalysisTracker::Scope* current,
       }
       break;
     }
+    case IrOpcode::kMapGuard: {
+      Node* object = current->ValueInput(0);
+      const VirtualObject* vobject = current->GetVirtualObject(object);
+      if (vobject && !vobject->HasEscaped()) {
+        current->MarkForDeletion();
+      }
+      break;
+    }
     case IrOpcode::kStateValues:
     case IrOpcode::kFrameState:
       // These uses are always safe.