Fix classes that have too many virtuals for inline constructors.

components/history/core/browser/history_service_observer.h

Index: components/history/core/browser/history_service_observer.h
diff --git a/components/history/core/browser/history_service_observer.h b/components/history/core/browser/history_service_observer.h
index 4e4438735b165c81cfef7952ee7845a13f7d5983..a9d716bd123dcf499c2a100e79c6af9108cea865 100644
--- a/components/history/core/browser/history_service_observer.h
+++ b/components/history/core/browser/history_service_observer.h
@@ -15,7 +15,6 @@ class HistoryService;
 
 class HistoryServiceObserver {
  public:
-  HistoryServiceObserver() {}
   virtual ~HistoryServiceObserver() {}
 
   // Called when user visits an URL.
@@ -73,6 +72,9 @@ class HistoryServiceObserver {
   virtual void OnKeywordSearchTermDeleted(HistoryService* history_service,
                                           URLID url_id) {}
 
+ protected:
+  HistoryServiceObserver() {}
+
  private:
   DISALLOW_COPY_AND_ASSIGN(HistoryServiceObserver);
 };