Restrict number of BlimpContents to [0, 1]

blimp/client/core/contents/blimp_contents_manager.h

Index: blimp/client/core/contents/blimp_contents_manager.h
diff --git a/blimp/client/core/contents/blimp_contents_manager.h b/blimp/client/core/contents/blimp_contents_manager.h
index 9b58e76186bb9cd19145a2b6161ca04b2639c05f..a19e6efdaa4a8016d1aea7d995c680007c3e8b29 100644
--- a/blimp/client/core/contents/blimp_contents_manager.h
+++ b/blimp/client/core/contents/blimp_contents_manager.h
@@ -23,6 +23,8 @@ class BlimpContentsManager {
   ~BlimpContentsManager();
 
   // Builds a BlimpContentsImpl and notifies the engine.
+  // TODO(mlliu): Currently we want to have a single BlimpContents. If there is
+  // an existing contents, return nullptr (http://crbug.com/642558).
   std::unique_ptr<BlimpContentsImpl> CreateBlimpContents();
 
   // The caller can query the contents through its id.
@@ -55,6 +57,10 @@ class BlimpContentsManager {
   NavigationFeature* navigation_feature_;
   TabControlFeature* tab_control_feature_;
 
+  // TODO(mlliu): Currently we want to have a single BlimpContents. Remove this
+  // when it supports multiple tabs (http://crbug.com/642558).
+  bool tab_exists_ = false;
+
   base::WeakPtrFactory<BlimpContentsManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(BlimpContentsManager);