Add a fake cast extension for testing.

chrome/test/data/extensions/tray_cast/background.js

Index: chrome/test/data/extensions/tray_cast/background.js
diff --git a/chrome/test/data/extensions/tray_cast/background.js b/chrome/test/data/extensions/tray_cast/background.js
new file mode 100644
index 0000000000000000000000000000000000000000..a80f5c2255cdd031b67fa81af21d86441107962e
--- /dev/null
+++ b/chrome/test/data/extensions/tray_cast/background.js
@@ -0,0 +1,72 @@
+var backgroundSetup = {}
+
+tryCreateActivity = function(id, title, tabId) {

[achuithb, 2015/07/09 21:40:10]

Add a function comment

[jdufault, 2015/07/09 23:09:06]

Done.

+  if (id === undefined || title === undefined || tabId === undefined)
+    return null;
+
+  return {
+    "id": id,
+    "title": title,
+    "tabId": tabId
+  };
+}
+
+var receiversActivities = [];
+// Add a new receiver. |activityTitle| and |activityTabId| are optional
+// parameters.
+addReceiver = function(id, receiverName, activityTitle, activityTabId) {
+  receiversActivities.push({
+    "activity": tryCreateActivity(id, activityTitle, activityTabId),
+    "receiver": {
+      "id": id,
+      "name": receiverName
+    }
+  });
+}
+// Required API method.
+getMirrorCapableReceiversAndActivities = function() {
+  if (this !== backgroundSetup)

[achuithb, 2015/07/09 21:40:10]

What's this about? Add a comment

[jdufault, 2015/07/09 23:09:06]

Done.

+    throw 'this !== backgroundSetup';
+
+  return receiversActivities;
+}
+
+var stopMirroringReason = "";
+var stopMirroringCalled = false;
+wasStopMirroringCalledWithUserStop = function() {

[achuithb, 2015/07/09 21:40:10]

function comment

[jdufault, 2015/07/09 23:09:06]

It'd be something along the lines of "Returns true if stop mirroring was called
with 'user-stop'", which is essentially a rephrasing of the method name.

If you feel strongly, I can add a comment, but I'd prefer not to since the
method name is already so verbose.

+  return stopMirroringCalled && stopMirroringReason == 'user-stop';
+}
+// Required API method.
+stopMirroring = function(reason) {
+  if (this !== backgroundSetup)
+    throw 'this !== backgroundSetup';
+
+  stopMirroringReason = reason;
+  stopMirroringCalled = true;
+  for (item of receiversActivities) {
+    if (item.activity != null)

[achuithb, 2015/07/09 21:40:10]

Is it necessary to add any checks here that at least one item.activity is
non-null?

[jdufault, 2015/07/09 23:09:06]

Sure, I can do that. It will help verify that stopMirroring is not called when
there are no receivers.

+      item.activity = null;
+  }
+}
+
+var launchTabId = 1;
+var launchTabTitle = "Fake Cast";
+var launchDesktopMirroringReceiverId = "";
+getLaunchDesktopMirroringReceiverId = function() {
+  return launchDesktopMirroringReceiverId;
+}
+// Required API method.
+launchDesktopMirroring = function(receiverId) {
+  if (this !== backgroundSetup)
+    throw 'this !== backgroundSetup';
+
+  launchDesktopMirroringReceiverId = receiverId;
+
+  for (item of receiversActivities) {
+    if (item.receiver.id == receiverId) {

[achuithb, 2015/07/09 21:40:10]

Is it necessary to add any extra checks here to ensure that at least one
receiver id matches?

[jdufault, 2015/07/09 23:09:06]

I'm not sure what value this will add. The testing code checks the calling value
via `getLaunchDesktopMirroringReceiverId()`.

+      item.activity =
+        tryCreateActivity(receiverId, launchTabId, launchTabTitle);
+      break;
+    }
+  }
+}