MD Settings: Simplify settings-dropdown-menu

chrome/browser/resources/settings/prefs/selectable_pref_behavior.js

Index: chrome/browser/resources/settings/prefs/selectable_pref_behavior.js
diff --git a/chrome/browser/resources/settings/prefs/selectable_pref_behavior.js b/chrome/browser/resources/settings/prefs/selectable_pref_behavior.js
new file mode 100644
index 0000000000000000000000000000000000000000..137f019ad02b82058d2f17d36e9bbc504354a408
--- /dev/null
+++ b/chrome/browser/resources/settings/prefs/selectable_pref_behavior.js
@@ -0,0 +1,47 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @fileoverview Behavior to convert between a pref value and a string.
+ */
+
+/** @polymerBehavior */
+var SelectablePrefBehavior = {
+  /**
+   * @param {string} value
+   * @return {*}
+   */
+  toPrefValue: function(value) {

[stevenjb, 2015/11/11 02:04:22]

nit: Even tho we're using Closure to type values, it's still less obvious that
|value| needs to be a string, so I think the code will be more readable if we
name this stringToPrefValue.

+    if (!this.pref)
+      return undefined;

[stevenjb, 2015/11/11 02:04:22]

I have a slight preference for passing 'this.pref' to these, since |pref| is not
defined in the behavior, but I don't feel too strongly about that. If we do
implement this as-is, we should document that any element using this behavior is
expected to have a |pref| member of type PrefObject.

[michaelpg, 2015/11/11 20:29:21]

I see your point, but then, should something like this be a global ("static")
utility rather than a behavior?

[stevenjb, 2015/11/11 20:42:28]

It certainly could be. In this case maybe that would be better?
'PrefUtil.StringToPrefValue(this.pref, value)'?

Unless we plan to use these within data binding (like e.g. we do with i18n())
that might be simpler.

+    if (this.pref.type == chrome.settingsPrivate.PrefType.NUMBER) {
+      var n = parseInt(value, 10);
+      if (isNaN(n)) {
+        console.error('Bad selected name for numerical pref: ' + value);
+        return undefined;
+      }
+      return n;
+    } else if (this.pref.type == chrome.settingsPrivate.PrefType.BOOLEAN) {
+      return value == 'true';
+    } else {
+      assert(this.pref.type == chrome.settingsPrivate.PrefType.STRING);
+      return value;
+    }
+  },
+
+  /**
+   * Returns the string value of the pref.
+   * @return {string}
+   */
+  prefToString: function() {
+    if (!this.pref)
+      return '';
+    if (this.pref.type == chrome.settingsPrivate.PrefType.NUMBER ||
+        this.pref.type == chrome.settingsPrivate.PrefType.BOOLEAN) {
+      return this.pref.value.toString();
+    }
+    assert(this.pref.type == chrome.settingsPrivate.PrefType.STRING);
+    return /** @type {string} */(this.pref.value);
+  },
+};