MD Settings: Fix label visibility in subpage search fields

ui/webui/resources/cr_elements/cr_search_field/cr_search_field_behavior.js

Index: ui/webui/resources/cr_elements/cr_search_field/cr_search_field_behavior.js
diff --git a/ui/webui/resources/cr_elements/cr_search_field/cr_search_field_behavior.js b/ui/webui/resources/cr_elements/cr_search_field/cr_search_field_behavior.js
index 68c15d4ff6146d481f0c60d025cb8dfaa58dc179..491bbb53d601264a1059da22c8096280ae59a584 100644
--- a/ui/webui/resources/cr_elements/cr_search_field/cr_search_field_behavior.js
+++ b/ui/webui/resources/cr_elements/cr_search_field/cr_search_field_behavior.js
@@ -19,6 +19,12 @@ var CrSearchFieldBehavior = {
       value: '',
     },
 
+    hasSearchText: {
+      type: Boolean,
+      reflectToAttribute: true,
+      value: false,
+    },
+
     /** @private */
     lastValue_: {
       type: String,
@@ -49,6 +55,8 @@ var CrSearchFieldBehavior = {
   setValue: function(value, opt_noEvent) {
     var searchInput = this.getSearchInput();
     searchInput.value = value;
+
+    this.onSearchTermInput();
     this.onValueChanged_(value, !!opt_noEvent);
   },
 
@@ -57,6 +65,15 @@ var CrSearchFieldBehavior = {
   },
 
   /**
+   * Update the state of the search field whenever the underlying input value
+   * changes. Unlike onsearch or onkeypress, this is reliably called immediately
+   * after any change, whether the result of user input or JS modification.
+   */
+  onSearchTermInput: function() {
+    this.hasSearchText = this.$.searchInput.value != '';
+  },
+
+  /**
    * Updates the internal state of the search field based on a change that has
    * already happened.
    * @param {string} newValue