Update comment for Browser::TYPE_APP

Better document which kinds of "apps" use this type.

See also go/cros-app-types

Bug: none
Change-Id: Ia6b799915bc17a40ea151a9feda5a2e2da7ec3d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587869
Commit-Queue: James Cook <jamescook@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Auto-Submit: James Cook <jamescook@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836739}

chrome/browser/ui/browser.h

@@ -131,7 +131,13 @@ class Browser : public TabStripModelObserver,
     TYPE_NORMAL,
     // Popup browser.
     TYPE_POPUP,
-    // App browser.
+    // App browser. Specifically, one of these:
+    // * Web app; comes in different flavors but is backed by the same code:
+    //   - Progressive Web App (PWA)
+    //   - Shortcut app (from 3-dot menu > More tools > Create shortcut)
+    //   - System web app (Chrome OS only)
+    // * Legacy packaged app ("v1 packaged app")
+    // * Hosted app (e.g. the Web Store "app" preinstalled on Chromebooks)
     TYPE_APP,
     // Devtools browser.
     TYPE_DEVTOOLS,