[Media Router WebUI] Filter out domain-less pseudo sinks from sink count

We were counting hidden (domain-less) pseudo sinks in the device count
metric, which was inflating the data. This CL subtracts such pseudo
sinks from the count.

Bug: 868139

Change-Id: Ic389b89390ed28f9ebb25af60be452ff2df47c7c
Reviewed-on: https://chromium-review.googlesource.com/1152350Reviewed-by: Derek Cheng <imcheng@chromium.org>
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578822}

chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js

@@ -465,8 +465,13 @@ Polymer({
       // sinks.
       this.async(function() {
         this.justOpened_ = false;
+        // |pseudoSinks_| does not contain pseudo sinks without a domain, so it
+        // cannot be used for calculating the number of real sinks.
+        var realSinks = this.allSinks.filter(function(sink) {
+          return !sink.isPseudoSink;
+        });
         this.fire('report-sink-count', {
-          sinkCount: this.allSinks.length - this.pseudoSinks_.length,
+          sinkCount: realSinks.length,
         });
       }, 3000 /* 3 seconds */);