[PresentationAPI] Implementing start/joinSession from WebPresentationClient to PresentationService.

content/shell/renderer/test_runner/mock_presentation_client.cc

Index: content/shell/renderer/test_runner/mock_presentation_client.cc
diff --git a/content/shell/renderer/test_runner/mock_presentation_client.cc b/content/shell/renderer/test_runner/mock_presentation_client.cc
index 02012bca821851a92d8e266e1e6c1aedfc266c70..46dc5d019064ae04832365c3636ea8a3e6331c95 100644
--- a/content/shell/renderer/test_runner/mock_presentation_client.cc
+++ b/content/shell/renderer/test_runner/mock_presentation_client.cc
@@ -50,6 +50,20 @@ void MockPresentationClient::setController(
   controller_ = controller;
 }
 
+void MockPresentationClient::startSession(
+    const blink::WebString& presentationUrl,
+    const blink::WebString& presentationId,
+    blink::WebPresentationSessionCreateCallback* callback) {
+  NOTIMPLEMENTED();
+}
+
+void MockPresentationClient::joinSession(
+    const blink::WebString& presentationUrl,
+    const blink::WebString& presentationId,
+    blink::WebPresentationSessionCreateCallback* callback) {
+  NOTIMPLEMENTED();
+}
+
 void MockPresentationClient::updateAvailableChangeWatched(bool watched) {
   if (!watched)
     return;