Reland "[Nav Experiment] Fix form repost detection in WKBasedNavigationManager."

This is a reland of 091e44cb.

It fixes the regression in
WebUITestCase/testChromeURLBackAndForwardAndReloadNavigation. WebUI
needs special handling in reload because calling [WKWebView -reload]
simply reloads WKWebView.URL (which is an app-specific URL in this case)
and results in a provisional load failure.

The other suspected test failure
(ContextMenuJsTest.LinkOfTextWithCalloutNone) is not caused by the
original CL. It seems to be flaky. It failed again after the revert:
https://luci-milo.appspot.com/buildbot/internal.bling.main/iphone11-device-x64/2532
and it failed before the original CL was checked in:
https://luci-milo.appspot.com/buildbot/internal.bling.main/iphone11-device-x64/2504

Original change's description:
> [Nav Experiment] Fix form repost detection in WKBasedNavigationManager.
>
> This CL moves form repost detection for WKBasedNavigationManager to
> in |webView:decidePolicyForNavigationAction|, where WKWebView gives a
> clear signal about form reposting (WKNavigationTypeFormResubmitted).
> This allows simplifying reload for WKBasedNavigationManager to directly
> delegating to [WKWebView reload].
>
> FormsTestCase now pass with WKBasedNavigationManager.
>
> Bug: 807428,705020
> Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
> Change-Id: Ia35978c42b21405a3749d1764a0485cde9c805d2
> Reviewed-on: https://chromium-review.googlesource.com/894892
> Commit-Queue: Danyao Wang <danyao@chromium.org>
> Reviewed-by: Eugene But <eugenebut@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#533692}t

Bug: 807428
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: If0bb1c907472ec402931c69f347c9259907c4f28
Reviewed-on: https://chromium-review.googlesource.com/899916Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Danyao Wang <danyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534163}

ios/web/web_state/ui/crw_web_controller.mm

@@ -1943,7 +1943,16 @@ registerLoadRequestForURL:(const GURL&)requestURL
     } else {
       self.currentNavItem->SetTransitionType(
           ui::PageTransition::PAGE_TRANSITION_RELOAD);
-      [self loadCurrentURL];
+      if (web::GetWebClient()->IsSlimNavigationManagerEnabled() &&
+          !web::GetWebClient()->IsAppSpecificURL(
+              net::GURLWithNSURL(_webView.URL))) {
+        // New navigation manager can delegate directly to WKWebView to reload
+        // for non-app-specific URLs. The necessary navigation states will be
+        // updated in WKNavigationDelegate callbacks.
+        [_webView reload];
+      } else {
+        [self loadCurrentURL];
+      }
     }
   }
 }
@@ -4191,11 +4200,32 @@ registerLoadRequestForURL:(const GURL&)requestURL
   // retrieved state will be pending until |didCommitNavigation| callback.
   [self updatePendingNavigationInfoFromNavigationAction:action];
 
-  // If this is a placeholder navigation, pass through.
-  if (web::GetWebClient()->IsSlimNavigationManagerEnabled() &&
-      IsPlaceholderUrl(requestURL)) {
-    decisionHandler(WKNavigationActionPolicyAllow);
-    return;
+  if (web::GetWebClient()->IsSlimNavigationManagerEnabled()) {
+    // If this is a placeholder navigation, pass through.
+    if (IsPlaceholderUrl(requestURL)) {
+      decisionHandler(WKNavigationActionPolicyAllow);
+      return;
+    }
+
+    // WKBasedNavigationManager doesn't use |loadCurrentURL| for reload or back/
+    // forward navigation. So this is the first point where a form repost would
+    // be detected. Display the confirmation dialog.
+    if ([action.request.HTTPMethod isEqual:@"POST"] &&
+        (action.navigationType == WKNavigationTypeFormResubmitted ||
+         action.navigationType == WKNavigationTypeBackForward)) {
+      _webStateImpl->ShowRepostFormWarningDialog(
+          base::BindBlockArc(^(bool shouldContinue) {
+            if (shouldContinue) {
+              decisionHandler(WKNavigationActionPolicyAllow);
+            } else {
+              decisionHandler(WKNavigationActionPolicyCancel);
+              if (action.targetFrame.mainFrame) {
+                [_pendingNavigationInfo setCancelled:YES];
+              }
+            }
+          }));
+      return;
+    }
   }
 
   // Invalid URLs should not be loaded.
@@ -5303,6 +5333,7 @@ registerLoadRequestForURL:(const GURL&)requestURL
   // If the request is form submission or resubmission, then prompt the
   // user before proceeding.
   DCHECK(repostedForm);
+  DCHECK(!web::GetWebClient()->IsSlimNavigationManagerEnabled());
   _webStateImpl->ShowRepostFormWarningDialog(
       base::BindBlockArc(^(bool shouldContinue) {
         if (shouldContinue)