Fabric: Support for optional `key` parameter to register/retrieve in ContextContainer

Summary:
@public
We need this in case when we want to store several intances of the same class in the container.

Reviewed By: mdvacca

Differential Revision: D8814808

fbshipit-source-id: 78ab15d78cf3878d03bf0a45bc42b968d87435e7

ReactCommon/fabric/uimanager/ContextContainer.h

@@ -24,20 +24,37 @@ using SharedContextContainer = std::shared_ptr<ContextContainer>;
 class ContextContainer final {
 
 public:
+  /*
+   * Registers an instance of the particular type `T` in the container.
+   * If `key` parameter is specified, the instance is registered
+   * by `{type, key}` pair.
+   */
   template<typename T>
-  void registerInstance(std::shared_ptr<T> instance) {
+  void registerInstance(std::shared_ptr<T> instance, const std::string &key = "") {
     std::lock_guard<std::mutex> lock(mutex_);
-    instances_.insert({std::type_index(typeid(T)), instance});
+    instances_.insert({
+      {std::type_index(typeid(T)), key},
+      instance
+    });
   }
 
+  /*
+   * Returns a previously registered instance of the particular type `T`.
+   * If `key` parameter is specified, the lookup will be performed
+   * by {type, key} pair.
+   */
   template<typename T>
-  std::shared_ptr<T> getInstance() const {
+  std::shared_ptr<T> getInstance(const std::string &key = "") const {
     std::lock_guard<std::mutex> lock(mutex_);
-    return std::static_pointer_cast<T>(instances_.at(std::type_index(typeid(T))));
+    return std::static_pointer_cast<T>(instances_.at({std::type_index(typeid(T)), key}));
   }
 
 private:
-  std::unordered_map<std::type_index, std::shared_ptr<void>> instances_;
+  std::unordered_map<
+    std::pair<std::type_index, std::string>,
+    std::shared_ptr<void>
+  > instances_;
+
   mutable std::mutex mutex_;
 };