[iOS] Don't reset fullscreen state for same-document navigations.

Bug: 834131
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I7a3bb44da51bdd3aac19ff8da559d4178e0fe168
Reviewed-on: https://chromium-review.googlesource.com/1017231
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552164}

ios/chrome/browser/ui/fullscreen/fullscreen_web_state_observer.mm

@@ -13,6 +13,7 @@
 #import "ios/web/public/navigation_item.h"
 #import "ios/web/public/navigation_manager.h"
 #include "ios/web/public/ssl_status.h"
+#import "ios/web/public/web_state/navigation_context.h"
 #import "ios/web/public/web_state/ui/crw_web_view_proxy.h"
 #import "ios/web/public/web_state/web_state.h"
 
@@ -88,8 +89,10 @@ void FullscreenWebStateObserver::DidFinishNavigation(
   web_state->GetWebViewProxy().shouldUseViewContentInset =
       force_content_inset ||
       web_state->GetContentsMimeType() == "application/pdf";
-  // Reset the model so that the toolbar is visible for the new page.
-  model_->ResetForNavigation();
+  // Reset the model so that the toolbar is visible when navigating to a new
+  // document.
+  if (!navigation_context->IsSameDocument())
+    model_->ResetForNavigation();
   // Disable fullscreen if there is a problem with the SSL status.
   SetDisableFullscreenForSSL(ShouldDisableFullscreenForWebStateSSL(web_state));
 }

ios/chrome/browser/ui/fullscreen/fullscreen_web_state_observer_unittest.mm

@@ -69,6 +69,19 @@ TEST_F(FullscreenWebStateObserverTest, ResetForNavigation) {
   EXPECT_EQ(model().progress(), 1.0);
 }
 
+// Tests that the FullscreenModel is not reset for a same-document navigation.
+TEST_F(FullscreenWebStateObserverTest, NoResetForSameDocument) {
+  // Simulate a scroll to 0.5 progress.
+  SimulateFullscreenUserScrollForProgress(&model(), 0.5);
+  EXPECT_EQ(model().progress(), 0.5);
+  // Simulate a same-document navigation and verify that the 0.5 progress hasn't
+  // been reset to 1.0.
+  web::FakeNavigationContext context;
+  context.SetIsSameDocument(true);
+  web_state().OnNavigationFinished(&context);
+  EXPECT_EQ(model().progress(), 0.5);
+}
+
 // Tests that the model is disabled when a load is occurring.
 TEST_F(FullscreenWebStateObserverTest, DisableDuringLoad) {
   EXPECT_TRUE(model().enabled());