Credential manager: Fixing missing stub declarations.

public/platform/WebCredentialManager.h

Index: public/platform/WebCredentialManager.h
diff --git a/public/platform/WebCredentialManager.h b/public/platform/WebCredentialManager.h
index bbd44ec64a05163cf039ef5f803777cb1c0e5f2f..9bd239acf34f2ab8c538681b1c1c342d0102430c 100644
--- a/public/platform/WebCredentialManager.h
+++ b/public/platform/WebCredentialManager.h
@@ -19,8 +19,8 @@ public:
     typedef WebCallbacks<WebCredential, WebCredentialManagerError> RequestCallbacks;
     typedef WebCallbacks<void, WebCredentialManagerError> NotificationCallbacks;
 
-    WebCredentialManager();
-    virtual ~WebCredentialManager();
+    WebCredentialManager() { }
+    virtual ~WebCredentialManager() { }
 
     // Ownership of the callback is transferred to the callee for each of the following methods.
     virtual void dispatchFailedSignIn(const WebCredential&, NotificationCallbacks*) { }