Fix chrome://extensions checkboxes

1. fix vertical alignment
2. fix text overlap in Hindi
3. fix text measuring function for Hindi (so the checkbox stays in one place when you check and uncheck it)

BUG=411805

Review URL: https://codereview.chromium.org/557553002

Cr-Commit-Position: refs/heads/master@{#293862}

chrome/browser/resources/extensions/extensions.css

@@ -360,10 +360,9 @@ html[dir=rtl] .extension-commands-config {
   -webkit-transition: opacity 200ms;
   height: 22px;
   opacity: 0.8;
-  position: absolute;
+  position: relative;
   right: 0;
-  top: 3px;
-  vertical-align: middle;
+  top: 6px;
 }
 
 html[dir='rtl'] #extension-settings .trash {

chrome/browser/resources/extensions/extensions.js

@@ -432,12 +432,15 @@ cr.define('extensions', function() {
     var measuringDiv = $('font-measuring-div');
     measuringDiv.textContent =
         loadTimeData.getString('extensionSettingsEnabled');
+    measuringDiv.className = 'enabled-text';
     var pxWidth = measuringDiv.clientWidth + trashWidth;
     measuringDiv.textContent =
         loadTimeData.getString('extensionSettingsEnable');
+    measuringDiv.className = 'enable-text';
     pxWidth = Math.max(measuringDiv.clientWidth + trashWidth, pxWidth);
     measuringDiv.textContent =
         loadTimeData.getString('extensionSettingsDeveloperMode');
+    measuringDiv.className = '';
     pxWidth = Math.max(measuringDiv.clientWidth, pxWidth);
 
     var style = document.createElement('style');