[Android] Alter ExternalNavigationHandlerTest's overriding of feature

Currently ExternalNavigationHandlerTest overrides the value of a
feature in ChromeFeatureList.java via the functionality that the latter
supports for enabling features in test contexts. However, we will be
porting the feature in question to be defined via a //components-level
ExternalIntentsFeatureList.java that will be as minimal as possible
(see crbug.com/1060097 for context); in particular, we do not want to
have to port over the functionality that supports enabling the feature
in a test. Thus, this CL changes the test to enable the production
functionality in question via an explicit testing API on
ExternalNavigationHandler.java.

Note that all of this will go away if/once the functionality is enabled
by default and the feature is removed altogether, which is work under
development (see crbug.com/839751).

Bug: 1031465
Change-Id: Ibcdf9e0e72b7c7564ee067625af7e0f4bb663d69
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2093607
Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749097}

chrome/android/java/src/org/chromium/chrome/browser/externalnav/ExternalNavigationHandler.java

@@ -358,6 +358,13 @@ public class ExternalNavigationHandler {
         return false;
     }
 
+    /** Wrapper of check against the feature to support overriding for testing. */
+    @VisibleForTesting
+    boolean blockExternalFormRedirectsWithoutGesture() {
+        return ChromeFeatureList.isEnabled(
+                ChromeFeatureList.INTENT_BLOCK_EXTERNAL_FORM_REDIRECT_NO_GESTURE);
+    }
+
     /**
      * http://crbug.com/149218: We want to show the intent picker for ordinary links, providing
      * the link is not an incoming intent from another application, unless it's a redirect.
@@ -383,8 +390,7 @@ public class ExternalNavigationHandler {
         // TODO(tedchoc): Remove the ChromeFeatureList check once we verify this change does
         //                not break the world.
         if (isRedirectFromFormSubmit && !incomingIntentRedirect && !params.hasUserGesture()
-                && ChromeFeatureList.isEnabled(
-                        ChromeFeatureList.INTENT_BLOCK_EXTERNAL_FORM_REDIRECT_NO_GESTURE)) {
+                && blockExternalFormRedirectsWithoutGesture()) {
             if (DEBUG) {
                 Log.i(TAG,
                         "Incoming form intent attempting to redirect without "

chrome/android/javatests/src/org/chromium/chrome/browser/externalnav/ExternalNavigationHandlerTest.java

@@ -59,8 +59,7 @@ import java.util.regex.Pattern;
 // clang-format off
 @DisableIf.Build(message = "Flaky on K - see https://crbug.com/851444",
         sdk_is_less_than = Build.VERSION_CODES.LOLLIPOP)
-@Features.EnableFeatures({ChromeFeatureList.CCT_EXTERNAL_LINK_HANDLING,
-        ChromeFeatureList.INTENT_BLOCK_EXTERNAL_FORM_REDIRECT_NO_GESTURE})
+@Features.EnableFeatures({ChromeFeatureList.CCT_EXTERNAL_LINK_HANDLING})
 public class ExternalNavigationHandlerTest {
     // clang-format on
     @Rule
@@ -140,7 +139,12 @@ public class ExternalNavigationHandlerTest {
 
     public ExternalNavigationHandlerTest() {
         mDelegate = new TestExternalNavigationDelegate();
-        mUrlHandler = new ExternalNavigationHandler(mDelegate);
+        mUrlHandler = new ExternalNavigationHandler(mDelegate) {
+            @Override
+            boolean blockExternalFormRedirectsWithoutGesture() {
+                return true;
+            }
+        };
     }
 
     @Before