Add comment to avoid using FeaturePromoBubbleView directly

As a stopgap before adding proper documentation, this comment
discourages use of FeaturePromoBubbleView and redirects users to
FeaturePromoController.

Bug: 1132335
Change-Id: Ia036dea11232645227d62124fd6683f1a74b32b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2431767Reviewed-by: Dana Fried <dfried@chromium.org>
Commit-Queue: Collin Baker <collinbaker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810710}

chrome/browser/ui/views/in_product_help/feature_promo_bubble_view.h

@@ -27,9 +27,12 @@ namespace views {
 class MdTextButton;
 }
 
+// NOTE: Avoid using this class directly. FeaturePromoController should
+// be used in almost all cases.
+//
 // The FeaturePromoBubbleView is a special BubbleDialogDelegateView for
-// in-product help which educates users about certain Chrome features in a
-// deferred context.
+// in-product help which educates users about certain Chrome features in
+// a deferred context.
 class FeaturePromoBubbleView : public views::BubbleDialogDelegateView {
  public:
   // Disallow copy and assign.
@@ -37,6 +40,9 @@ class FeaturePromoBubbleView : public views::BubbleDialogDelegateView {
   FeaturePromoBubbleView& operator=(const FeaturePromoBubbleView&) = delete;
   ~FeaturePromoBubbleView() override;
 
+  // NOTE: Please read comment above class. This method shouldn't be
+  // called in most cases.
+  //
   // Creates the promo. The returned pointer is only valid until the
   // widget is destroyed. It must not be manually deleted by the caller.
   static FeaturePromoBubbleView* Create(

chrome/browser/ui/views/in_product_help/feature_promo_controller.h

@@ -23,6 +23,12 @@ class FeaturePromoController {
   // components/feature_engagement/public/feature_list.cc and registered
   // with |FeaturePromoRegistry|. Note that this is different than the
   // feature that the IPH is showing for.
+  //
+  // For users that can't register their parameters with
+  // FeaturePromoRegistry, see
+  // |FeaturePromoControllerViews::MaybeShowPromoWithParams()|. Prefer
+  // statically registering params with FeaturePromoRegistry and using
+  // this method when possible.
   virtual bool MaybeShowPromo(const base::Feature& iph_feature) = 0;
 
   // Returns whether a bubble is showing for the given IPH. Note that if