Bug 1314016: Do not attempt to obtain wrapper and set MSAA ID on child document unless it was successfully added; r=tbsaunde

MozReview-Commit-ID: G4lDNxXtoVx

--HG--
extra : rebase_source : 833a13c5251e4e2c031bb63ae78851a2d7b3650a

dom/ipc/TabParent.cpp

@@ -938,7 +938,9 @@ TabParent::RecvPDocAccessibleConstructor(PDocAccessibleParent* aDoc,
     auto parentDoc = static_cast<a11y::DocAccessibleParent*>(aParentDoc);
     bool added = parentDoc->AddChildDoc(doc, aParentID);
 #ifdef XP_WIN
-    a11y::WrapperFor(doc)->SetID(aMsaaID);
+    if (added) {
+      a11y::WrapperFor(doc)->SetID(aMsaaID);
+    }
 #endif
     return added;
   } else {