[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 a374304bbeccff3459dc4982ebd92d0a460b319e..6bad6518fc0dd312c6436b76485174654adc873e 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
@@ -66,6 +66,11 @@ Polymer({
   ready: function() {
     this.$.clearFrom.menuOptions = this.clearFromOptions_;
     this.addWebUIListener(
+        'browsing-data-removing',
+        function(isRemoving) {
+          this.clearingInProgress_ = isRemoving;
+        }.bind(this));
+    this.addWebUIListener(
         'browsing-history-pref-changed',
         this.setAllowDeletingHistory_.bind(this));
     this.addWebUIListener(
@@ -74,10 +79,15 @@ Polymer({
     this.addWebUIListener(
         'update-counter-text',
         this.updateCounterText_.bind(this));
+  },
+
+  attached: function() {

[dpapad, 2016/07/08 18:04:42]

Nit: @override

     this.browserProxy_ =
         settings.ClearBrowsingDataBrowserProxyImpl.getInstance();
-    this.browserProxy_.initialize();
-    this.$.dialog.open();
+    this.browserProxy_.initialize().then(function() {
+      assert(typeof this.clearingInProgress_ == 'boolean');

[dpapad, 2016/07/08 18:04:42]

Why do we allow this boolean to have a tri-state (undefined, false, true),
instead of giving it a default value at line 53?

[Dan Beam, 2016/07/08 19:19:07]

because otherwise it's not clear the value is valid.

do you mean: you'd like to set clearingInProgress_ to true at first?

[dpapad, 2016/07/08 19:21:07]

Yes, I think in this case "true" is the appropriate default value.

[Dan Beam, 2016/07/08 19:27:44]

ultimately I don't care, but I think that leaving the value undefined ENSURES
(via the assert() I asked for) that this mechanism never breaks and that we're
open()ing the dialog in a valid state

+      this.$.dialog.open();
+    }.bind(this));
   },
 
   /**
@@ -138,7 +148,6 @@ Polymer({
        *     about other forms of browsing history before closing the dialog.
        */
       function(shouldShowNotice) {
-        this.clearingInProgress_ = false;
         this.showHistoryDeletionDialog_ = shouldShowNotice;
 
         if (!shouldShowNotice)