Introduce NavigationSimulator to use in unit tests

content/browser/frame_host/navigation_handle_impl.h

Index: content/browser/frame_host/navigation_handle_impl.h
diff --git a/content/browser/frame_host/navigation_handle_impl.h b/content/browser/frame_host/navigation_handle_impl.h
index ed4dc615fe406f2b4f6501252e78da729ac9ba42..e9cb20983e0c94bfd343b693d330b7b89ecdf3ad 100644
--- a/content/browser/frame_host/navigation_handle_impl.h
+++ b/content/browser/frame_host/navigation_handle_impl.h
@@ -95,6 +95,21 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
       bool started_from_context_menu);
   ~NavigationHandleImpl() override;
 
+  // Used to track the state the navigation is currently in.
+  enum State {
+    INITIAL = 0,
+    WILL_SEND_REQUEST,
+    DEFERRING_START,
+    WILL_REDIRECT_REQUEST,
+    DEFERRING_REDIRECT,
+    CANCELING,
+    WILL_PROCESS_RESPONSE,
+    DEFERRING_RESPONSE,
+    READY_TO_COMMIT,
+    DID_COMMIT,
+    DID_COMMIT_ERROR_PAGE,
+  };
+
   // NavigationHandle implementation:
   const GURL& GetURL() override;
   SiteInstance* GetStartingSiteInstance() override;
@@ -151,6 +166,9 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
 
   NavigationData* GetNavigationData() override;
 
+  // Used in tests.
+  State state_for_testing() const { return state_; }
+
   // The NavigatorDelegate to notify/query for various navigation events.
   // Normally this is the WebContents, except if this NavigationHandle was
   // created during a navigation to an interstitial page. In this case it will
@@ -331,21 +349,6 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
  private:
   friend class NavigationHandleImplTest;
 
-  // Used to track the state the navigation is currently in.
-  enum State {
-    INITIAL = 0,
-    WILL_SEND_REQUEST,
-    DEFERRING_START,
-    WILL_REDIRECT_REQUEST,
-    DEFERRING_REDIRECT,
-    CANCELING,
-    WILL_PROCESS_RESPONSE,
-    DEFERRING_RESPONSE,
-    READY_TO_COMMIT,
-    DID_COMMIT,
-    DID_COMMIT_ERROR_PAGE,
-  };
-
   NavigationHandleImpl(const GURL& url,
                        const std::vector<GURL>& redirect_chain,
                        FrameTreeNode* frame_tree_node,