Fix HistoryTabHelper::DidFinishNavigation crash.

Per DidFinishNavigation documentation, this callback can be called for
replaced navigations, in which case NavigationContext::HasCommitted will
return false.

This CL adds an early return to HistoryTabHelper::DidFinishNavigation
if the navigation was not committed.

Bug: 813024
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I7a0a1f180faae9715b4992d3f7b810e3287a7cda
Reviewed-on: https://chromium-review.googlesource.com/984376Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547043}

ios/chrome/browser/history/history_tab_helper.mm

@@ -97,6 +97,10 @@ void HistoryTabHelper::DidFinishNavigation(
     return;
   }
 
+  if (!navigation_context->HasCommitted()) {
+    return;
+  }
+
   DCHECK(web_state->GetNavigationManager()->GetVisibleItem());
   web::NavigationItem* visible_item =
       web_state_->GetNavigationManager()->GetVisibleItem();

ios/chrome/browser/tabs/tab_unittest.mm

@@ -223,6 +223,7 @@ class TabTest : public BlockCleanupTest {
     context2.SetUrl(redirect_url);
     web_state_impl_->OnNavigationStarted(&context2);
     [tab_ navigationManagerImpl]->CommitPendingItem();
+    context2.SetHasCommitted(true);
     web_state_impl_->UpdateHttpResponseHeaders(redirect_url);
     web_state_impl_->OnNavigationFinished(&context2);
     web_state_impl_->SetIsLoading(true);