[PresentationAPI] Added plumbing for start/joinSession from JS to platform

Source/modules/presentation/Presentation.cpp

Index: Source/modules/presentation/Presentation.cpp
diff --git a/Source/modules/presentation/Presentation.cpp b/Source/modules/presentation/Presentation.cpp
index 1dd3bcc41dd3e792cab64a91641207d2469fa8f3..6213d4f13505572dec88ee06057941372f2fe0df 100644
--- a/Source/modules/presentation/Presentation.cpp
+++ b/Source/modules/presentation/Presentation.cpp
@@ -15,6 +15,7 @@
 #include "modules/EventTargetModules.h"
 #include "modules/presentation/AvailableChangeEvent.h"
 #include "modules/presentation/PresentationController.h"
+#include "modules/presentation/PresentationSessionClientCallbacks.h"
 
 namespace blink {
 
@@ -52,6 +53,7 @@ ExecutionContext* Presentation::executionContext() const
 DEFINE_TRACE(Presentation)
 {
     visitor->trace(m_session);
+    visitor->trace(m_openSessions);
     RefCountedGarbageCollectedEventTargetWithInlineData<Presentation>::trace(visitor);
     DOMWindowProperty::trace(visitor);
 }
@@ -65,7 +67,14 @@ ScriptPromise Presentation::startSession(ScriptState* state, const String& prese
 {
     RefPtrWillBeRawPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(state);
     ScriptPromise promise = resolver->promise();
-    resolver->reject(DOMException::create(NotSupportedError, "The method is not supported yet."));
+
+    PresentationController* controller = presentationController();
+    if (!controller) {
+        resolver->reject(DOMException::create(InvalidStateError, "The object is no longer attached to the frame."));
+        return promise;
+    }
+    controller->startSession(presentationUrl, presentationId, new PresentationSessionClientCallbacks(resolver, this));
+
     return promise;
 }
 
@@ -73,7 +82,14 @@ ScriptPromise Presentation::joinSession(ScriptState* state, const String& presen
 {
     RefPtrWillBeRawPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(state);
     ScriptPromise promise = resolver->promise();
-    resolver->reject(DOMException::create(NotSupportedError, "The method is not supported yet."));
+
+    PresentationController* controller = presentationController();
+    if (!controller) {
+        resolver->reject(DOMException::create(InvalidStateError, "The object is no longer attached to the frame."));
+        return promise;
+    }
+    controller->joinSession(presentationUrl, presentationId, new PresentationSessionClientCallbacks(resolver, this));
+
     return promise;
 }
 
@@ -129,6 +145,11 @@ bool Presentation::isAvailableChangeWatched() const
     return hasEventListeners(EventTypeNames::availablechange);
 }
 
+void Presentation::registerSession(PresentationSession* session)
+{
+    m_openSessions.add(session);
+}
+
 PresentationController* Presentation::presentationController()
 {
     if (!frame())