[Presentation API] Resolve PresentationRequest::reconnect() with existing presentation connection i…

third_party/WebKit/LayoutTests/presentation/resources/presentation-service-mock.js

Index: third_party/WebKit/LayoutTests/presentation/resources/presentation-service-mock.js
diff --git a/third_party/WebKit/LayoutTests/presentation/resources/presentation-service-mock.js b/third_party/WebKit/LayoutTests/presentation/resources/presentation-service-mock.js
index 6df94aa574e1037beb3a420494d3cac2b6b65a48..790bba54640068ec5d79729cf1d15bbfcbd931b9 100644
--- a/third_party/WebKit/LayoutTests/presentation/resources/presentation-service-mock.js
+++ b/third_party/WebKit/LayoutTests/presentation/resources/presentation-service-mock.js
@@ -29,6 +29,13 @@ let presentationServiceMock = loadMojoModules(
               error: null,
           });
         }
+
+        joinSession(urls) {
+          return Promise.resolve({
+              sessionInfo: { url: urls[0], id: 'fakeSessionId' },
+              error: null,
+          });
+        }
       }
 
       return new PresentationServiceMock(mojo.frameInterfaces);