[PresentationAPI] Added on-session-message handler.

content/renderer/presentation/presentation_session_client.cc

Index: content/renderer/presentation/presentation_session_client.cc
diff --git a/content/renderer/presentation/presentation_session_client.cc b/content/renderer/presentation/presentation_session_client.cc
index 62b28527c29e816ecbeca8700f684b8f7bfbf5ae..be8c754d8946ad6f9aea479c4104aed094369fe6 100644
--- a/content/renderer/presentation/presentation_session_client.cc
+++ b/content/renderer/presentation/presentation_session_client.cc
@@ -15,6 +15,12 @@ PresentationSessionClient::PresentationSessionClient(
       id_(blink::WebString::fromUTF8(session_info->id)) {
 }
 
+PresentationSessionClient::PresentationSessionClient(const mojo::String& url,
+                                                     const mojo::String& id)
+    : url_(blink::WebString::fromUTF8(url)),
+      id_(blink::WebString::fromUTF8(id)) {
+}
+
 PresentationSessionClient::~PresentationSessionClient() {
 }