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, 44 insertions, 0 deletions

diff --git a/Firebase/Core/FIRDependency.m b/Firebase/Core/FIRDependency.m
new file mode 100644
index 0000000..f979984
--- /dev/null
+++ b/Firebase/Core/FIRDependency.m
@@ -0,0 +1,44 @@
+/*
+ * 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.
+ */
+
+#import "Private/FIRDependency.h"
+
+@interface FIRDependency ()
+
+- (instancetype)initWithProtocol:(Protocol *)protocol isRequired:(BOOL)required;
+
+@end
+
+@implementation FIRDependency
+
++ (instancetype)dependencyWithProtocol:(Protocol *)protocol {
+  return [[self alloc] initWithProtocol:protocol isRequired:YES];
+}
+
++ (instancetype)dependencyWithProtocol:(Protocol *)protocol isRequired:(BOOL)required {
+  return [[self alloc] initWithProtocol:protocol isRequired:required];
+}
+
+- (instancetype)initWithProtocol:(Protocol *)protocol isRequired:(BOOL)required {
+  self = [super init];
+  if (self) {
+    _protocol = protocol;
+    _isRequired = required;
+  }
+  return self;
+}
+
+@end