Add FirebaseCore component interoperability. (#1437)

* Add FirebaseCore component interoperability.

This puts in place the system that will allow SDKs to register with
Core and retrieve functionalities provided by other SDKs.

* Updated documentation.

* Add copywrite, fix log messages.

* Explicitly import headers from Private dir

1 files changed, 38 insertions, 0 deletions

diff --git a/Firebase/Core/Private/FIRComponentRegistrant.h b/Firebase/Core/Private/FIRComponentRegistrant.h
new file mode 100644
index 0000000..ad2cad2
--- /dev/null
+++ b/Firebase/Core/Private/FIRComponentRegistrant.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRComponentRegistrant_h
+#define FIRComponentRegistrant_h
+
+#import <Foundation/Foundation.h>
+
+@class FIRComponent;
+
+NS_ASSUME_NONNULL_BEGIN
+
+/// Describes functionality for SDKs registering components in the `FIRComponentContainer`.
+NS_SWIFT_NAME(ComponentRegistrant)
+@protocol FIRComponentRegistrant
+
+/// Returns one or more FIRComponents that will be registered in
+/// FIRApp and participate in dependency resolution and injection.
++ (NSArray<FIRComponent *> *)componentsToRegister;
+
+@end
+
+NS_ASSUME_NONNULL_END
+
+#endif /* FIRComponentRegistrant_h */