[Media Router] Implement JoinRoute + update CreateRoute API.

chrome/browser/media/router/media_router.mojom

Index: chrome/browser/media/router/media_router.mojom
diff --git a/chrome/browser/media/router/media_router.mojom b/chrome/browser/media/router/media_router.mojom
index e67b327f5571e0419906741eeae7448f81d9ac6e..33ca365fd3e6679b3d695870f1334024820b8393 100644
--- a/chrome/browser/media/router/media_router.mojom
+++ b/chrome/browser/media/router/media_router.mojom
@@ -84,12 +84,35 @@ struct Issue {
 // chrome/browser/media/router/media_router.h
 interface MediaRouter {
   // Initiates a media route from |media_source| to |sink_id|.
+  // The presentation ID of the route created will be |presentation_id|, but it
+  // may be overridden by a provider implementation. The presentation ID will

[mark a. foltz, 2015/06/10 23:18:51]

Does any provider actually do this?  Last time I checked the Cast MRP did not
need to override the id for new routes.

[imcheng (use chromium acct), 2015/06/11 22:49:12]

I remember in the Start + Join doc that there was a use case where presentation
ID was overridden by the Cast MRP?

+  // be used by the presentation API to refer to the created route.
+  // |origin| and |tab_id| may be passed in for enforcing same-origin and/or
+  // same-tab scopes and are optional.
+  // Since int types cannot be made optional, use -1 as |tab_id| in cases where
+  // it is not applicable.
   // If the operation was successful, |route| will be defined and
   //     |error_text| will be null.
   // If the operation failed, |route| will be null and |error_text|
   //     will be set.
-  CreateRoute(string media_source, string sink_id) =>
-      (MediaRoute? route, string? error_text);
+  CreateRoute(string media_source,
+              string sink_id,
+              string presentation_id,

[mark a. foltz, 2015/06/10 23:18:51]

This might be better named default_presentation_id or original_presentation_id.

[imcheng (use chromium acct), 2015/06/11 22:49:12]

Done.

+              string? origin,
+              int32 tab_id) => (MediaRoute? route, string? error_text);
+
+  // Joins an established route given by |presentation_id|
+  // with |media_source|.
+  // |origin| and |tab_id| are used for validating same-origin/tab scopes and
+  // are optional. (See CreateRoute for additional documentation)
+  // If the operation was successful, |route| will be defined and
+  //     |error_text| will be null.
+  // If the operation failed, |route| will be null and |error_text|
+  //     will be set.
+  JoinRoute(string media_source,
+            string presentation_id,
+            string? origin,
+            int32 tab_id) => (MediaRoute? route, string? error_text);
 
   // Closes the route specified by |route_id|.
   CloseRoute(string route_id);