[MD settings] disable clear browsing data while it is running

chrome/browser/resources/settings/clear_browsing_data_dialog/clear_browsing_data_dialog.js

Index: chrome/browser/resources/settings/clear_browsing_data_dialog/clear_browsing_data_dialog.js
diff --git a/chrome/browser/resources/settings/clear_browsing_data_dialog/clear_browsing_data_dialog.js b/chrome/browser/resources/settings/clear_browsing_data_dialog/clear_browsing_data_dialog.js
index b094d5983c685e4c116ee19ba15728a88f21cd38..54dd748c66f5784c2f29e6b07f0d00737838b6f8 100644
--- a/chrome/browser/resources/settings/clear_browsing_data_dialog/clear_browsing_data_dialog.js
+++ b/chrome/browser/resources/settings/clear_browsing_data_dialog/clear_browsing_data_dialog.js
@@ -50,7 +50,10 @@ Polymer({
     },
 
     /** @private */
-    clearingInProgress_: Boolean,
+    clearingInProgress_: {
+      type: Boolean,
+      value: true,  /* Default to true to avoid potential race condition. */
+    },
 
     /** @private */
     showHistoryDeletionDialog_: {
@@ -69,6 +72,9 @@ Polymer({
         'browsing-history-pref-changed',
         this.setAllowDeletingHistory_.bind(this));
     this.addWebUIListener(
+        'clearing-browsing-data',
+        this.setClearingInProgress_.bind(this));
+    this.addWebUIListener(
         'update-footer',
         this.updateFooter_.bind(this));
     this.addWebUIListener(
@@ -94,6 +100,14 @@ Polymer({
   },
 
   /**
+   * @param {boolean} inProgress Whether clearing browsing data is in progress.
+   * @private
+   */
+  setClearingInProgress_: function(inProgress) {
+    this.clearingInProgress_ = inProgress;
+  },
+
+  /**
    * Updates the footer to show only those sentences that are relevant to this
    * user.
    * @param {boolean} syncing Whether the user is syncing data.