Coordinators are now notified when moving to a parent coordinator.

BUG=none
R=rohitrao@chromium.org

Review-Url: https://codereview.chromium.org/2755653002
Cr-Commit-Position: refs/heads/master@{#457797}

ios/clean/chrome/browser/browser_coordinator+internal.h

@@ -59,6 +59,12 @@
 // |coordinator| isn't a child of the receiver, this method does nothing.
 - (void)removeChildCoordinator:(BrowserCoordinator*)coordinator;
 
+// Called when this coordinator moves to a new parent coordinator.  Subclasses
+// can override this method to run code that requires a configured
+// CoordinatorContext.
+- (void)coordinatorDidMoveToParentCoordinator:
+    (BrowserCoordinator*)parentCoordinator;
+
 // Called when a child coordinator did start. This is a blank template method.
 // Subclasses can override this method when they need to know when their
 // children start.

ios/clean/chrome/browser/browser_coordinator.mm

@@ -72,6 +72,7 @@
   coordinator.parentCoordinator = self;
   coordinator.browser = self.browser;
   coordinator.context.baseViewController = self.viewController;
+  [coordinator coordinatorDidMoveToParentCoordinator:self];
 }
 
 - (BrowserCoordinator*)overlayCoordinator {
@@ -126,6 +127,11 @@
   coordinator.parentCoordinator = nil;
 }
 
+- (void)coordinatorDidMoveToParentCoordinator:
+    (BrowserCoordinator*)parentCoordinator {
+  // Default implementation is a no-op.
+}
+
 - (void)childCoordinatorDidStart:(BrowserCoordinator*)childCoordinator {
   // Default implementation is a no-op.
 }