chakrashim: ref count data sent to SetEmbedderData

JS Objects passed to SetEmbedderData need to have JsAddRef/JsRelease
called, otherwise they could be GC'd prematurely.

Fixes: nodejs#97

deps/chakrashim/src/jsrtcontextshim.cc

@@ -504,6 +504,15 @@ void ContextShim::SetAlignedPointerInEmbedderData(int index, void * value) {
     if (embedderData.size() < minSize) {
       embedderData.resize(minSize);
     }
+
+    // ensure reference counting, otherwise objects can be GC'd.  JsAddRef/
+    // JsRelease will handle cases if the pointer is not valid for ref counts.
+    void * oldValue = embedderData[index];
+    if (oldValue != nullptr) {
+      JsRelease(oldValue, nullptr);
+    }
+    JsAddRef(value, nullptr);
+
     embedderData[index] = value;
   } catch(const std::exception&) {
   }