Expand comments on ExternalNavigationHandler#shouldKeepIntentRedirect…

…InApp

I was having trouble figuring out what this function was for and whether
it was still necessary (it is). So I've re-written the comments and
expanded on them to hopefully be clearer.

Change-Id: Iceaa8db9a76d7c8f2e3a3112c0e478307a0a713a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3774834
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Commit-Queue: Yaron Friedman <yfriedman@chromium.org>
Auto-Submit: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1026215}

components/external_intents/android/java/src/org/chromium/components/external_intents/ExternalNavigationHandler.java

@@ -1403,11 +1403,15 @@ private void onUserDecidedWhetherToLaunchIncognitoIntent(final boolean shouldLau
     }
 
     /**
-     * If some third-party app launched this app with an intent, and the URL got redirected, and the
-     * user explicitly chose this app over other intent handlers, stay in the app unless there was a
-     * new intent handler after redirection or the app cannot handle it internally any more.
-     * Custom tabs are an exception to this rule, since at no point, the user sees an intent picker
-     * and "picking the Chrome app" is handled inside the support library.
+     * If another app, or the user, chose to launch this app for an intent, we should keep that
+     * navigation within this app through redirects until it resolves to a new app or external
+     * protocol given this app was intentionally chosen. Custom tabs always explicitly target the
+     * browser and this issue is handled elsewhere through
+     * {@link RedirectHandler#intentPrefersToStayInChrome()}.
+     *
+     * Usually this covers cases like https://www.youtube.com/ redirecting to
+     * https://m.youtube.com/. Note that this isn't covered by {@link #shouldStayWithinHost()} as
+     * for intent navigation there is no previously committed URL.
      */
     private boolean shouldKeepIntentRedirectInApp(ExternalNavigationParams params,
             boolean incomingIntentRedirect, List<ResolveInfo> resolvingInfos,
@@ -1416,7 +1420,7 @@ private boolean shouldKeepIntentRedirectInApp(ExternalNavigationParams params,
                 && !params.getRedirectHandler().isFromCustomTabIntent()
                 && !params.getRedirectHandler().hasNewResolver(
                         resolvingInfos, (Intent intent) -> queryIntentActivities(intent))) {
-            if (DEBUG) Log.i(TAG, "Custom tab redirect no handled");
+            if (DEBUG) Log.i(TAG, "Intent navigation with no new handlers.");
             return true;
         }
         return false;