[NTP] Defer the voice JS file

It will be executed "when the page has finished parsing" which seems right
for this script.

Bug: 868432
Change-Id: Icb0fb03518aca785c7a3d8583bcbfaecd4cb1487
Reviewed-on: https://chromium-review.googlesource.com/1154365Reviewed-by: Kristi Park <kristipark@chromium.org>
Commit-Queue: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579295}

chrome/browser/resources/local_ntp/local_ntp.html

@@ -8,12 +8,10 @@
   <link rel="stylesheet" href="chrome-search://local-ntp/local-ntp.css"></link>
   <link rel="stylesheet" href="chrome-search://local-ntp/voice.css"></link>
   <link rel="stylesheet" href="chrome-search://local-ntp/custom-backgrounds.css"></link>
-  <script src="chrome-search://local-ntp/local-ntp.js"
-      {{LOCAL_NTP_INTEGRITY}}></script>
-  <script src="chrome-search://local-ntp/voice.js"
-      {{LOCAL_NTP_VOICE_INTEGRITY}}></script>
   <script src="chrome-search://local-ntp/custom-backgrounds.js"
       {{LOCAL_NTP_CUSTOM_BG_INTEGRITY}}></script>
+  <script src="chrome-search://local-ntp/local-ntp.js"
+      {{LOCAL_NTP_INTEGRITY}}></script>
   <meta charset="utf-8">
   <meta name="google" value="notranslate">
 </head>
@@ -165,5 +163,8 @@
   </dialog>
 
   <div id="one-google-end-of-body"></div>
+
+  <script defer src="chrome-search://local-ntp/voice.js"
+      {{LOCAL_NTP_VOICE_INTEGRITY}}></script>
 </body>
 </html>