[blimp] Add support for having multiple tabs

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 31e8bf6fd936d9293866bd7d543017a7ed1841cb..07b922eb5e2dacd4aacc9366a20c8d1a2c856206 100644
--- a/blimp/client/core/contents/blimp_contents_manager.h
+++ b/blimp/client/core/contents/blimp_contents_manager.h
@@ -62,6 +62,10 @@ class BlimpContentsManager {
   void EraseObserverFromMap(int id);
   base::WeakPtr<BlimpContentsManager> GetWeakPtr();
 
+  // The ID to use whenever a new BlimpContentsImpl is created. Incremented
+  // after each use.
+  int next_blimp_contents_id_ = 0;
+
   // BlimpContentsManager owns the BlimpContentsDeletionObserver for the
   // contents it creates, with the content id being the key to help manage the
   // lifetime of the observers.