[DevTools] Remove unnecessary emulation checkboxes and simplify UX.

LayoutTests/inspector/device-emulation/device-emulation-test.js

 function setMetaViewport()
 {
     var VIEWPORTS = {
         "w=320": "width=320",
         "w=dw": "width=device-width",
         "w=980": "width=980",
         "none": "no viewport (desktop site)"
     };
 
     var viewport = VIEWPORTS["none"];
@@ skipping 174 matching lines @@
     InspectorTest.evaluateInPage("dumpMetrics(" + full + ")", callback);
 }
 
 InspectorTest.applyEmulationAndReload = function(enabled, width, height, deviceScaleFactor, viewport, callback)
 {
     InspectorTest.addSniffer(WebInspector.overridesSupport, "_deviceMetricsOverrideAppliedForTest", emulateCallback);
     if (enabled)
         WebInspector.overridesSupport.emulateDevice(new WebInspector.OverridesSupport.Device(width + "x" + height + "x" + deviceScaleFactor + "x1x1", ""));
     else
         WebInspector.overridesSupport.reset();
+    WebInspector.overridesSupport.settings.emulationEnabled.set(enabled);
 
     function emulateCallback()
     {
         var warning = WebInspector.overridesSupport.warningMessage();
         if (warning)
             InspectorTest._deviceEmulationResults.push("Emulation warning: " + warning);
         InspectorTest.navigate(InspectorTest._deviceEmulationPageUrl + "?" + viewport, callback);
     }
 };
 
@@ skipping 17 matching lines @@
     InspectorTest.emulateAndGetMetrics(width, height, deviceScaleFactor, viewport, callback);
 
     function callback()
     {
         InspectorTest.addResult(InspectorTest._deviceEmulationResults.join("\n"));
         InspectorTest.completeTest();
     }
 };
 
 };