Updated not keep overriding our emulation metrics

lib/page.js

@@ -1324,12 +1324,28 @@ module.exports = exports = function(options) {
 
   };
 
+  // handle the params
+  var lastConfig = null;
+
   /**
   * Handles setting emulation information
   **/
   ChromePage.emulate = function(params, fn) {
 
-    if(!params || (params || {}).width == 1280) return fn(null);
+    if(lastConfig && 
+        lastConfig.width == params.width && 
+          lastConfig.height == params.height) {
+
+      // nope 
+      return fn(null);
+
+    } else {
+
+      if(!lastConfig) lastConfig = {};
+      lastConfig.height = params.height;
+      lastConfig.width = params.width;
+
+    }
 
     // add to clear any other emulation
     return Emulation.clearDeviceMetricsOverride()