Do not allow GuestViewManager to (re)use an instance ID that was already removed.

chrome/browser/guest_view/guest_view_manager.h

Index: chrome/browser/guest_view/guest_view_manager.h
diff --git a/chrome/browser/guest_view/guest_view_manager.h b/chrome/browser/guest_view/guest_view_manager.h
index df643dc3b093d7d8f10e5ea33d5af08272bf02a1..26117f7f690d290a8cb3c0896c3efffee5c7e4ee 100644
--- a/chrome/browser/guest_view/guest_view_manager.h
+++ b/chrome/browser/guest_view/guest_view_manager.h
@@ -7,6 +7,7 @@
 
 #include <map>
 
+#include "base/gtest_prod_util.h"
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "content/public/browser/browser_plugin_guest_manager.h"
@@ -56,8 +57,11 @@ class GuestViewManager : public content::BrowserPluginGuestManager,
  private:
   friend class GuestViewBase;
   friend class GuestWebContentsObserver;
+  friend class TestGuestViewManager;
+  FRIEND_TEST_ALL_PREFIXES(GuestViewManagerTest, AddRemove);
 
-  void AddGuest(int guest_instance_id,
+  // Returns true if adding the instance was successful.
+  bool AddGuest(int guest_instance_id,
                 content::WebContents* guest_web_contents);
 
   void RemoveGuest(int guest_instance_id);
@@ -89,6 +93,16 @@ class GuestViewManager : public content::BrowserPluginGuestManager,
   GuestInstanceMap guest_web_contents_by_instance_id_;
 
   int current_instance_id_;
+
+  // Any instance ID whose number not greater than this was removed via
+  // RemoveGuest.
+  // This is used so that we don't have store all removed instance IDs in
+  // |removed_instance_ids_|.
+  int last_instance_id_removed_;
+  // The remaining instance IDs that are greater than
+  // |last_instance_id_removed_| are kept here.
+  std::set<int> removed_instance_ids_;
+
   content::BrowserContext* context_;
 
   DISALLOW_COPY_AND_ASSIGN(GuestViewManager);