Expose loading state from Blimp to Tab

blimp/client/core/contents/blimp_navigation_controller_delegate.h

Index: blimp/client/core/contents/blimp_navigation_controller_delegate.h
diff --git a/blimp/client/core/contents/blimp_navigation_controller_delegate.h b/blimp/client/core/contents/blimp_navigation_controller_delegate.h
index e50f8435d053048c1f3a2a56520d578d01ca4265..3fa817080c8771b286d49d8fda611c33aba111b1 100644
--- a/blimp/client/core/contents/blimp_navigation_controller_delegate.h
+++ b/blimp/client/core/contents/blimp_navigation_controller_delegate.h
@@ -17,9 +17,14 @@ class BlimpNavigationControllerDelegate {
  public:
   virtual ~BlimpNavigationControllerDelegate() = default;
 
+  // TODO(dtrainor): Pull apart this method into more fine grained notifications
+  // or add an enum to detect exactly which state changed.
   // Informs the delegate that navigation state has changed.
   virtual void OnNavigationStateChanged() = 0;
 
+  // Informs the delegate that navigation loading has started or stopped.
+  virtual void OnLoadingStateChanged(bool loading) = 0;
+
  protected:
   BlimpNavigationControllerDelegate() {}