request log filtering: add i18n prompt

src/_locales/en/messages.json

@@ -35,6 +35,10 @@
     "message":"µBlock — Network request log",
     "description":"Title for the network request log window"
   },
+  "statsFilterPrompt":{
+    "message":"filter log entries",
+    "description": "English: filter log entries"
+  },
   "aboutPageName":{
     "message":"About",
     "description":"appears as tab name in dashboard"

src/devtool-log.html

@@ -10,7 +10,7 @@
 <div id="toolbar">
     <span id="reload" class="button fa">&#xf021;</span>
     <span id="clear" class="button fa">&#xf12d;</span>
-    <span id="filterButton" class="button fa">&#xf0b0;</span><input id="filterExpression" type="text">
+    <span id="filterButton" class="button fa">&#xf0b0;</span><input id="filterExpression" type="text" placeholder="statsFilterPrompt">
     </div>
 <div id="content">
     <table><tbody></tbody></table>
@@ -18,6 +18,7 @@
 <script src="js/vapi-common.js"></script>
 <script src="js/vapi-client.js"></script>
 <script src="js/udom.js"></script>
+<script src="js/i18n.js"></script>
 <script src="js/devtool-log.js"></script>
 </body>
 </html>

src/js/i18n.js

@@ -36,6 +36,12 @@ uDom.onLoad(function() {
             elem.attr('title', title);
         }
     });
+    uDom('[placeholder]').forEach(function(elem) {
+        var placeholder = vAPI.i18n(elem.attr('placeholder'));
+        if ( placeholder ) {
+            elem.attr('placeholder', placeholder);
+        }
+    });
     uDom('[data-i18n-tip]').forEach(function(elem) {
         elem.attr(
             'data-tip',