Bug 1367715: Check for IClientSecurity in a11y QueryInterface implementations; r=surkov

MozReview-Commit-ID: FwGEq5GLom1

--HG--
extra : rebase_source : 73e2e1e494e75cb1126583ca947208025a533690

accessible/windows/msaa/AccessibleWrap.cpp

@@ -118,6 +118,14 @@ AccessibleWrap::QueryInterface(REFIID iid, void** ppv)
 
   *ppv = nullptr;
 
+  if (IID_IClientSecurity == iid) {
+    // Some code might QI(IID_IClientSecurity) to detect whether or not we are
+    // a proxy. Right now that can potentially happen off the main thread, so we
+    // look for this condition immediately so that we don't trigger other code
+    // that might not be thread-safe.
+    return E_NOINTERFACE;
+  }
+
   if (IID_IUnknown == iid)
     *ppv = static_cast<IAccessible*>(this);
   else if (IID_IDispatch == iid || IID_IAccessible == iid)

accessible/windows/sdn/sdnAccessible.cpp

@@ -39,6 +39,14 @@ sdnAccessible::QueryInterface(REFIID aREFIID, void** aInstancePtr)
     return E_FAIL;
   *aInstancePtr = nullptr;
 
+  if (aREFIID == IID_IClientSecurity) {
+    // Some code might QI(IID_IClientSecurity) to detect whether or not we are
+    // a proxy. Right now that can potentially happen off the main thread, so we
+    // look for this condition immediately so that we don't trigger other code
+    // that might not be thread-safe.
+    return E_NOINTERFACE;
+  }
+
   if (aREFIID == IID_ISimpleDOMNode) {
     *aInstancePtr = static_cast<ISimpleDOMNode*>(this);
     AddRef();