Fix iOS orientation detection

developer.html and index.html used a different class name for the "Please rotate
your device" tag, and the start button. This caused the JS to throw exceptions when
running the orientation detection code.

So standardize these classes and ids between developer.html and index.html.

Author: smfr

MotionMark/developer.html

@@ -124,8 +124,8 @@ <h3>Time measurement method:</h3>
                     Attempting to detect system frame rate: <span>0</span> FPS (in progress).
                 </p>
                 <div class="start-benchmark">
-                    <p class="hidden">Please rotate the device to orientation before starting.</p>
-                    <button id="run-benchmark" onclick="benchmarkController.startBenchmark()">Run benchmark</button>
+                    <p class="portrait-orientation-check hidden">Please rotate the device to orientation before starting.</p>
+                    <button id="start-button" onclick="benchmarkController.startBenchmark()">Run benchmark</button>
                 </div>
             </div>
         </section>

MotionMark/resources/debug-runner/debug-runner.js

@@ -601,7 +601,7 @@ Utilities.extendObject(window.benchmarkController, {
 
     updateStartButtonState: function()
     {
-        var startButton = document.getElementById("run-benchmark");
+        var startButton = document.getElementById("start-button");
         if ("isInLandscapeOrientation" in this && !this.isInLandscapeOrientation) {
             startButton.disabled = true;
             return;

MotionMark/resources/runner/motionmark.js

@@ -521,15 +521,16 @@ window.benchmarkController = {
     {
         benchmarkController.isInLandscapeOrientation = match.matches;
         if (match.matches)
-            document.querySelector(".start-benchmark p").classList.add("hidden");
+            document.querySelector(".portrait-orientation-check").classList.add("hidden");
         else
-            document.querySelector(".start-benchmark p").classList.remove("hidden");
+            document.querySelector(".portrait-orientation-check").classList.remove("hidden");
+
         benchmarkController.updateStartButtonState();
     },
 
     updateStartButtonState: function()
     {
-        document.getElementById("run-benchmark").disabled = !this.isInLandscapeOrientation;
+        document.getElementById("start-button").disabled = !this.isInLandscapeOrientation;
     },
 
     _startBenchmark: function(suites, options, frameContainerID)