Change the battery-status layout tests to use JS mocks.

third_party/WebKit/LayoutTests/battery-status/resources/mock-battery-monitor.js

+"use strict";
+
+let mockBatteryMonitor = loadMojoModules(
+    'mockBatteryMonitor',
+    ['device/battery/battery_monitor.mojom',
+     'device/battery/battery_status.mojom',
+     'mojo/public/js/router',
+    ]).then(mojo => {
+  let [batteryMonitor, batteryStatus, router] = mojo.modules;
+
+  class MockBatteryMonitor extends batteryMonitor.BatteryMonitor.stubClass {
+    constructor(serviceRegistry) {
+      super();
+      serviceRegistry.addServiceOverrideForTesting(
+          batteryMonitor.BatteryMonitor.name,
+          handle => this.connect_(handle));
+
+      this.serviceRegistry_ = serviceRegistry;
+      this.pendingRequests_ = [];
+      this.status_ = null;
+    }
+
+    connect_(handle) {
+      this.router_ = new router.Router(handle);
+      this.router_.setIncomingReceiver(this);
+    }
+
+    queryNextStatus() {
+      let result = new Promise(resolve => this.pendingRequests_.push(resolve));
+      this.runCallbacks_();
+      return result;
+    }
+
+    updateBatteryStatus(charging, chargingTime, dischargingTime, level) {
+      this.status_ = new batteryStatus.BatteryStatus();
+      this.status_.charging = charging;
+      this.status_.charging_time = chargingTime;
+      this.status_.discharging_time = dischargingTime;
+      this.status_.level = level;
+      this.runCallbacks_();
+    }
+
+    runCallbacks_() {
+      if (!this.status_ || !this.pendingRequests_.length)
+        return;
+
+      while (this.pendingRequests_.length) {
+        this.pendingRequests_.pop()({status: this.status_});
+      }
+      this.status_ = null;
+    }
+

[Yuki, 2016/03/30 02:39:46]

nit: no need this empty line?

[Sam McNally, 2016/03/30 03:15:32]

Done.

+  }
+  return new MockBatteryMonitor(mojo.serviceRegistry);
+});
+
+let batteryInfo;

[Yuki, 2016/03/30 02:39:46]

I think we don't need this declaration here.

Let's add 'let' on line 72.

+let mockBatteryInfo;

[Yuki, 2016/03/30 02:39:46]

Maybe better to rename this variable to |lastSetMockBatteryInfo| or so?
and should be used only in this file.

[Sam McNally, 2016/03/30 03:15:33]

Done.

+
+function setAndFireMockBatteryInfo(charging, chargingTime, dischargingTime,
+                                   level) {
+  mockBatteryInfo = { charging: charging,
+                      chargingTime: chargingTime,
+                      dischargingTime: dischargingTime,
+                      level: level };
+  mockBatteryMonitor.then(mock => mock.updateBatteryStatus(
+      charging, chargingTime, dischargingTime, level));
+}
+
+// compare obtained battery values with the mock values
+function checkBatteryInfo(batteryManager) {

[Yuki, 2016/03/30 02:39:46]

Maybe better to rename this function to |testIfBatteryStatusIsUpToDate| or so?
It's not clear what the function is checking.

[Sam McNally, 2016/03/30 03:15:33]

Done.

+  batteryInfo = batteryManager;
+  shouldBeDefined("batteryInfo");
+  shouldBeDefined("mockBatteryInfo");
+  shouldBe('batteryInfo.charging', 'mockBatteryInfo.charging');
+  shouldBe('batteryInfo.chargingTime', 'mockBatteryInfo.chargingTime');
+  shouldBe('batteryInfo.dischargingTime', 'mockBatteryInfo.dischargingTime');
+  shouldBe('batteryInfo.level', 'mockBatteryInfo.level');
+}
+
+function batteryStatusFailure() {
+  testFailed('failed to successfully resolve the promise');
+  setTimeout(finishJSTest, 0);
+}
+
+let ready = mockBatteryMonitor.then();

[Yuki, 2016/03/30 02:39:46]

|ready| is too much general as a name of a global variable.

I'd suggest
    let mockBatteryMonitorLoader = loadMojoModules(...);
    var mockBatteryMonitor = mockBatteryMonitor.then();
or something like that.

Also, I think |let| here is a little confusing because it's intended to be used
as a global variable, not a local / block-scope variable.

[Sam McNally, 2016/03/30 03:15:32]

Done.