Add content public APIs for Presentation API.

content/public/browser/content_browser_client.h

Index: content/public/browser/content_browser_client.h
diff --git a/content/public/browser/content_browser_client.h b/content/public/browser/content_browser_client.h
index d97a87b2d427508961d2973e1f2cbb606a7a872c..61f6a2688053dbf1f3a510ae7d2305833d11adfe 100644
--- a/content/public/browser/content_browser_client.h
+++ b/content/public/browser/content_browser_client.h
@@ -96,6 +96,7 @@ class MediaObserver;
 class NavigatorConnectContext;
 class NavigatorConnectServiceFactory;
 class PlatformNotificationService;
+class PresentationServiceDelegate;
 class QuotaPermissionContext;
 class RenderFrameHost;
 class RenderProcessHost;
@@ -602,6 +603,11 @@ class CONTENT_EXPORT ContentBrowserClient {
       RenderFrameHost* render_frame_host,
       blink::WebPageVisibilityState* visibility_state) {}
 
+  // Allows an embedder to provide its own PresentationServiceDelegate
+  // implementation. Returns nullptr if unavailable.
+  virtual PresentationServiceDelegate* GetPresentationServiceDelegate(
+      WebContents* web_contents);
+
 #if defined(OS_POSIX) && !defined(OS_MACOSX)
   // Populates |mappings| with all files that need to be mapped before launching
   // a child process.