Credential manager: Fixing missing stub declarations.

https://src.chromium.org/viewvc/blink?view=rev&revision=180040 introduced
the WebCredentialManager interface, but neglected to create default
constructor/destructor implementations. This trivial patch corrects that
oversight.

BUG=400674
TBR=tkent@chromium.org

Review URL: https://codereview.chromium.org/466713002

git-svn-id: svn://svn.chromium.org/blink/trunk@180067 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/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*) { }