[ios] Fix page restoration placeholder

This CL fixes two bugs in the page restoration placeholder:

1) The alpha of the placeholder was not previously being reset to 1.0.

2) The page restoration placeholder was only being shown at the start
of a navigation. This means that the user will open a tab, it will
momentarily show blank (since the page has not yet been restored)
before showing the black/white placeholder. Now the black/white page
will show immediately as the user enters the tab.

Bug: 927843
Change-Id: If8ad4c60e05c84a240182316484e2657d46efaf0
Reviewed-on: https://chromium-review.googlesource.com/c/1450438
Commit-Queue: edchin <edchin@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628579}

ios/chrome/browser/web/page_placeholder_tab_helper.h

@@ -43,6 +43,8 @@ class PagePlaceholderTabHelper
   explicit PagePlaceholderTabHelper(web::WebState* web_state);
 
   // web::WebStateObserver overrides:
+  void WasShown(web::WebState* web_state) override;
+  void WasHidden(web::WebState* web_state) override;
   void DidStartNavigation(web::WebState* web_state,
                           web::NavigationContext* navigation_context) override;
   void PageLoaded(

ios/chrome/browser/web/page_placeholder_tab_helper.mm

@@ -42,6 +42,16 @@ void PagePlaceholderTabHelper::CancelPlaceholderForNextNavigation() {
   }
 }
 
+void PagePlaceholderTabHelper::WasShown(web::WebState* web_state) {
+  if (add_placeholder_for_next_navigation_) {
+    AddPlaceholder();
+  }
+}
+
+void PagePlaceholderTabHelper::WasHidden(web::WebState* web_state) {
+  RemovePlaceholder();
+}
+
 void PagePlaceholderTabHelper::DidStartNavigation(
     web::WebState* web_state,
     web::NavigationContext* navigation_context) {
@@ -84,18 +94,22 @@ void PagePlaceholderTabHelper::AddPlaceholder() {
   __weak UIImageView* weak_placeholder_view = placeholder_view_;
   __weak UIView* weak_web_state_view = web_state_->GetView();
   __weak id<CRWWebViewProxy> web_view_proxy = web_state_->GetWebViewProxy();
-  SnapshotTabHelper::FromWebState(web_state_)
-      ->RetrieveGreySnapshot(^(UIImage* snapshot) {
-        CGRect frame = weak_web_state_view.frame;
-        UIEdgeInsets inset = web_view_proxy.contentInset;
-        frame.origin.x += inset.left;
-        frame.origin.y += inset.top;
-        frame.size.width -= (inset.right + inset.left);
-        frame.size.height -= (inset.bottom + inset.top);
-        weak_placeholder_view.frame = frame;
-        weak_placeholder_view.image = snapshot;
-        [weak_web_state_view addSubview:weak_placeholder_view];
-      });
+
+  SnapshotTabHelper* snapshotTabHelper =
+      SnapshotTabHelper::FromWebState(web_state_);
+  if (snapshotTabHelper) {
+    snapshotTabHelper->RetrieveGreySnapshot(^(UIImage* snapshot) {
+      CGRect frame = weak_web_state_view.frame;
+      UIEdgeInsets inset = web_view_proxy.contentInset;
+      frame.origin.x += inset.left;
+      frame.origin.y += inset.top;
+      frame.size.width -= (inset.right + inset.left);
+      frame.size.height -= (inset.bottom + inset.top);
+      weak_placeholder_view.frame = frame;
+      weak_placeholder_view.image = snapshot;
+      [weak_web_state_view addSubview:weak_placeholder_view];
+    });
+  }
 
   // Remove placeholder if it takes too long to load the page.
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
@@ -119,5 +133,6 @@ void PagePlaceholderTabHelper::RemovePlaceholder() {
       }
       completion:^(BOOL finished) {
         [weak_placeholder_view removeFromSuperview];
+        weak_placeholder_view.alpha = 1.0f;
       }];
 }

ios/chrome/browser/web/page_placeholder_tab_helper_unittest.mm

@@ -53,6 +53,36 @@ class PagePlaceholderTabHelperTest : public PlatformTest {
   UIView* web_state_view_ = nil;
 };
 
+// Tests that placeholder is not shown after WasShown() if it was not requested.
+TEST_F(PagePlaceholderTabHelperTest, TabShownAndPlaceholderNotShown) {
+  ASSERT_FALSE(tab_helper()->displaying_placeholder());
+  ASSERT_FALSE(tab_helper()->will_add_placeholder_for_next_navigation());
+  web_state_->WasShown();
+  EXPECT_FALSE(tab_helper()->displaying_placeholder());
+  EXPECT_FALSE(tab_helper()->will_add_placeholder_for_next_navigation());
+}
+
+// Tests that placeholder is shown after WasShown() if it was requested.
+TEST_F(PagePlaceholderTabHelperTest, TabShownAndPlaceholderShown) {
+  ASSERT_FALSE(tab_helper()->displaying_placeholder());
+  ASSERT_FALSE(tab_helper()->will_add_placeholder_for_next_navigation());
+  tab_helper()->AddPlaceholderForNextNavigation();
+  ASSERT_FALSE(tab_helper()->displaying_placeholder());
+  EXPECT_TRUE(tab_helper()->will_add_placeholder_for_next_navigation());
+  web_state_->WasShown();
+  EXPECT_TRUE(tab_helper()->displaying_placeholder());
+  EXPECT_TRUE(tab_helper()->will_add_placeholder_for_next_navigation());
+}
+
+// Tests that placeholder is removed after WasHidden().
+TEST_F(PagePlaceholderTabHelperTest, TabHiddenAndPlaceholderRemoved) {
+  tab_helper()->AddPlaceholderForNextNavigation();
+  web_state_->WasShown();
+  ASSERT_TRUE(tab_helper()->displaying_placeholder());
+  web_state_->WasHidden();
+  EXPECT_FALSE(tab_helper()->displaying_placeholder());
+}
+
 // Tests that placeholder is not shown after DidStartNavigation if it was not
 // requested.
 TEST_F(PagePlaceholderTabHelperTest, NotShown) {