Refactor NavigationHandleImpl::RegisterNavigationThrottles.

content/browser/frame_host/navigation_handle_impl.cc

Index: content/browser/frame_host/navigation_handle_impl.cc
diff --git a/content/browser/frame_host/navigation_handle_impl.cc b/content/browser/frame_host/navigation_handle_impl.cc
index 4f024e887254fe4a23cbcc25cc955ddb79c04f2c..009f8d10208b18b7a1d6b1677d259acb59d7920f 100644
--- a/content/browser/frame_host/navigation_handle_impl.cc
+++ b/content/browser/frame_host/navigation_handle_impl.cc
@@ -1098,50 +1098,43 @@ void NavigationHandleImpl::RunCompleteCallback(
 }
 
 void NavigationHandleImpl::RegisterNavigationThrottles() {
-  // Register the navigation throttles. The vector returned by
-  // CreateThrottlesForNavigation is not assigned to throttles_ directly because
-  // it would overwrite any throttles previously added with
-  // RegisterThrottleForTesting.
-  // TODO(carlosk, arthursonzogni): should simplify this to either use
-  // |throttles_| directly (except for the case described above) or
-  // |throttles_to_register| for registering all throttles.
-  std::vector<std::unique_ptr<NavigationThrottle>> throttles_to_register =
-      GetDelegate()->CreateThrottlesForNavigation(this);
+  // Note: |throttle_| might not be empty. Some NavigationThrottles might have
+  // been registered with RegisterThrottleForTesting. These must reside at the
+  // end of |throttles_|. TestNavigationManagerThrottle expects that the
+  // NavigationThrottles added for test are the last NavigationThrottles to
+  // execute. Take them out while appending the rest of the
+  // NavigationThrottles.
+  std::vector<std::unique_ptr<NavigationThrottle>> testing_throttles =
+      std::move(throttles_);
+
+  throttles_ = GetDelegate()->CreateThrottlesForNavigation(this);
 
   // Check for renderer-inititated main frame navigations to data URLs. This is
   // done first as it may block the main frame navigation altogether.
-  std::unique_ptr<NavigationThrottle> data_url_navigation_throttle =
-      DataUrlNavigationThrottle::CreateThrottleForNavigation(this);
-  if (data_url_navigation_throttle)
-    throttles_to_register.push_back(std::move(data_url_navigation_throttle));
-
-  std::unique_ptr<content::NavigationThrottle> ancestor_throttle =
-      content::AncestorThrottle::MaybeCreateThrottleFor(this);
-  if (ancestor_throttle)
-    throttles_.push_back(std::move(ancestor_throttle));
+  AddThrottle(DataUrlNavigationThrottle::CreateThrottleForNavigation(this));
 
-  std::unique_ptr<content::NavigationThrottle> form_submission_throttle =
-      content::FormSubmissionThrottle::MaybeCreateThrottleFor(this);
-  if (form_submission_throttle)
-    throttles_.push_back(std::move(form_submission_throttle));
+  AddThrottle(AncestorThrottle::MaybeCreateThrottleFor(this));
+  AddThrottle(FormSubmissionThrottle::MaybeCreateThrottleFor(this));
 
   // Check for mixed content. This is done after the AncestorThrottle and the
   // FormSubmissionThrottle so that when folks block mixed content with a CSP
   // policy, they don't get a warning. They'll still get a warning in the
   // console about CSP blocking the load.
-  std::unique_ptr<NavigationThrottle> mixed_content_throttle =
-      MixedContentNavigationThrottle::CreateThrottleForNavigation(this);
-  if (mixed_content_throttle)
-    throttles_to_register.push_back(std::move(mixed_content_throttle));
-
-  std::unique_ptr<NavigationThrottle> devtools_throttle =
-      RenderFrameDevToolsAgentHost::CreateThrottleForNavigation(this);
-  if (devtools_throttle)
-    throttles_to_register.push_back(std::move(devtools_throttle));
-
-  throttles_.insert(throttles_.begin(),
-                    std::make_move_iterator(throttles_to_register.begin()),
-                    std::make_move_iterator(throttles_to_register.end()));
+  AddThrottle(
+      MixedContentNavigationThrottle::CreateThrottleForNavigation(this));
+
+  AddThrottle(RenderFrameDevToolsAgentHost::CreateThrottleForNavigation(this));
+
+  // Insert all testing NavigationThrottles last.
+  throttles_.insert(throttles_.end(),
+                    std::make_move_iterator(testing_throttles.begin()),
+                    std::make_move_iterator(testing_throttles.end()));
+}
+
+void NavigationHandleImpl::AddThrottle(
+    std::unique_ptr<NavigationThrottle> throttle) {
+  if (throttle)
+    throttles_.push_back(std::move(throttle));
 }
 
 bool NavigationHandleImpl::IsSelfReferentialURL() {