[Cast MRP] Added workarounds for crashes in JoinSession().

There isn't a known repro, so this CL is a best effort to fix the
likely cause of the crashes.

Bug: 1114067
Change-Id: I2416be1f2eddef8c3a954146ea9c905f78421a29
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2343596
Commit-Queue: John Williams <jrw@chromium.org>
Auto-Submit: John Williams <jrw@chromium.org>
Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796130}

chrome/browser/media/router/providers/cast/cast_activity_manager.cc

@@ -322,7 +322,7 @@ void CastActivityManager::JoinSession(
       media_sink_service_->GetSinkById(activity->route().media_sink_id());
   if (!sink) {
     logger_->LogError(mojom::LogCategory::kRoute, kLoggerComponent,
-                      "Cannot find the sink to join with sind_id.",
+                      "Cannot find the sink to join with sink_id.",
                       activity->route().media_sink_id(),
                       cast_source.source_id(), presentation_id);
     std::move(callback).Run(base::nullopt, nullptr,
@@ -334,7 +334,26 @@ void CastActivityManager::JoinSession(
   mojom::RoutePresentationConnectionPtr presentation_connection =
       activity->AddClient(cast_source, origin, tab_id);
 
-  DCHECK(activity->session_id());
+  if (!activity->session_id()) {
+    // This should never happen, but it looks like maybe it does.  See
+    // crbug.com/1114067.
+    NOTREACHED();
+    static const char kErrorMessage[] = "Internal error: missing session ID";
+    // Checking for |logger_| here is pure paranoia, but this code only exists
+    // to fix a crash we can't reproduce, so creating even a tiny possibility of
+    // a different crash seems like a bad idea.
+    if (logger_) {
+      // The empty string parameters could have real values, but they're omitted
+      // out of an abundance of caution, and they're not especially relevant to
+      // this error anyway.
+      logger_->LogError(mojom::LogCategory::kRoute, kLoggerComponent,
+                        kErrorMessage, "", "", "");
+    }
+    std::move(callback).Run(base::nullopt, nullptr, kErrorMessage,
+                            RouteRequestResult::ResultCode::UNKNOWN_ERROR);
+    return;
+  }
+
   const CastSession* session =
       session_tracker_->GetSessionById(*activity->session_id());
   const std::string& client_id = cast_source.client_id();

chrome/browser/media/router/providers/cast/cast_media_route_provider.cc

@@ -162,6 +162,22 @@ void CastMediaRouteProvider::JoinRoute(const std::string& media_source,
     return;
   }
 
+  if (!activity_manager_) {
+    // This should never happen, but it looks like maybe it does.  See
+    // crbug.com/1114067.
+    NOTREACHED();
+    // This message will probably go unnoticed, but it's here to give some
+    // indication of what went wrong, since NOTREACHED() is compiled out of
+    // release builds.  It would be nice if we could log a message to |logger_|,
+    // but it's initialized in the same place as |activity_manager_|, so it's
+    // almost certainly not available here.
+    LOG(ERROR) << "missing activity manager";
+    std::move(callback).Run(base::nullopt, nullptr,
+                            "Internal error: missing activity manager",
+                            RouteRequestResult::ResultCode::UNKNOWN_ERROR);
+    return;
+  }
+
   activity_manager_->JoinSession(*cast_source, presentation_id, origin, tab_id,
                                  incognito, std::move(callback));
 }