Set tab_id when initiating mirroring from a Cast SDK site

A tab mirroring source from a Cast SDK enabled website (e.g. Google
Slides) uses the mirroring app ID rather than the tab mirroring URN.
We need to set the tab ID in CreateRoute() for those cases.

An alternative way to do this would be making IsTabMirroringSource()
return true for those cases, but there's code that assumes support for
the audio mirroring app (separate ID from the mirroring app) if
IsTabMirroringSource() is true, which wouldn't make sense given the app
ID would not be the same as one specified.

Bug: 1047788
Change-Id: I100ccbd881854ddbae33b94474761a816061573c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2033926Reviewed-by: Brandon Tolsch <btolsch@chromium.org>
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738203}

chrome/browser/media/router/mojo/media_router_mojo_impl.cc

@@ -327,10 +327,13 @@ void MediaRouterMojoImpl::CreateRoute(const MediaSource::Id& source_id,
                        presentation_id, origin, web_contents, timeout,
                        incognito, std::move(mr_callback)));
   } else {
-    const int tab_id =
-        source.IsTabMirroringSource()
-            ? sessions::SessionTabHelper::IdForTab(web_contents).id()
-            : -1;
+    int tab_id = -1;
+    // A Cast SDK enabled website (e.g. Google Slides) may use the mirroring app
+    // ID rather than the tab mirroring URN.
+    if (source.IsTabMirroringSource() ||
+        source.id().find(kMirroringAppUri) == 0) {
+      tab_id = sessions::SessionTabHelper::IdForTab(web_contents).id();
+    }
     media_route_providers_[provider_id]->CreateRoute(
         source_id, sink_id, presentation_id, origin, tab_id, timeout, incognito,
         std::move(mr_callback));

chrome/common/media_router/media_source.h

@@ -23,6 +23,10 @@ constexpr char kRemotePlaybackPresentationUrlScheme[] = "remote-playback";
 constexpr char kLegacyCastPresentationUrlPrefix[] =
     "https://google.com/cast#__castAppId__=";
 
+// A Cast SDK enabled website (e.g. Google Slides) may use the mirroring app ID
+// rather than the tab mirroring URN.
+constexpr char kMirroringAppUri[] = "cast:0F5096E8";
+
 // Strings used in presentation IDs by the Cast SDK implementation.
 // TODO(takumif): Move them out of this file, since they are not directly
 // related to MediaSource.