extensions: don't animate options dialog when loading.

Transitions are disabled while loading, so animations should be as well.

This happens when chrome://extensions/?options=<id> is navigated to,
which shows the dialog immediately.

R=kalman@chromium.org
BUG=none
TEST=load chrome://extensions/?options=<extension_id> and look for
     needless animation

Review URL: https://codereview.chromium.org/896283003

Cr-Commit-Position: refs/heads/master@{#314649}

chrome/browser/resources/extensions/extension_options_overlay.js

@@ -131,9 +131,10 @@ cr.define('extensions', function() {
         // the overlay. It is calculated by multiplying the pythagorean distance
         // between old and the new size (in px) with a constant speed of
         // 0.25 ms/px.
-        var animationTime = 0.25 * Math.sqrt(
-            Math.pow(newWidth - oldWidth, 2) +
-            Math.pow(newHeight - oldHeight, 2));
+        var loading = document.documentElement.classlist.contains('loading');
+        var animationTime = loading ? 0 :
+            0.25 * Math.sqrt(Math.pow(newWidth - oldWidth, 2) +
+                             Math.pow(newHeight - oldHeight, 2));
 
         if (animation)
           animation.cancel();