[Extensions Toolbar] Add a finch config for the redesign

chrome/browser/extensions/extension_action.cc

Index: chrome/browser/extensions/extension_action.cc
diff --git a/chrome/browser/extensions/extension_action.cc b/chrome/browser/extensions/extension_action.cc
index af9e8685934c872f5e0e5b4aa3cdab328156bc93..c6033e53f8fb2f48bf8ddb7643f433af4945d6ed 100644
--- a/chrome/browser/extensions/extension_action.cc
+++ b/chrome/browser/extensions/extension_action.cc
@@ -256,15 +256,20 @@ gfx::Image ExtensionAction::GetDefaultIconImage() const {
   if (default_icon_image_)
     return default_icon_image_->image();
 
-  // If the extension action redesign is enabled, we use a special placeholder
-  // icon (with the first letter of the extension name) rather than the default
-  // (puzzle piece).
-  if (extensions::FeatureSwitch::extension_action_redesign()->IsEnabled()) {
-    return extensions::ExtensionIconPlaceholder::CreateImage(
-        extension_misc::EXTENSION_ICON_ACTION, extension_name_);
+  if (placeholder_icon_image_.IsEmpty()) {
+    // If the extension action redesign is enabled, we use a special placeholder
+    // icon (with the first letter of the extension name) rather than the
+    // default (puzzle piece).
+    if (extensions::FeatureSwitch::extension_action_redesign()->IsEnabled()) {
+      placeholder_icon_image_ =

[Devlin, 2015/09/21 23:28:15]

This was necessary because of a test that re-fetching the icon doesn't send back
a different instance.  I'm not sure it really matters, but I guess this has the
potential to be slightly faster.  The "mutable" in the .h is sad, but not
unreasonable or unprecedented, and taking the "const" off this method makes a
lot of other things blow up.

We could also deal with the churn and take the const off, decide we don't mind
the regeneration (alter the test), or initialize these on construction.  Lemme
know your preference. :)

+          extensions::ExtensionIconPlaceholder::CreateImage(
+              extension_misc::EXTENSION_ICON_ACTION, extension_name_);
+    } else {
+      placeholder_icon_image_ = GetDefaultIcon();
+    }
   }
 
-  return GetDefaultIcon();
+  return placeholder_icon_image_;
 }
 
 bool ExtensionAction::HasPopupUrl(int tab_id) const {