[iOS] Created flag for contentInset-based fullscreen implementation.

This CL adds a flag that forces the CRWWebViewContentView to always use
the WKScrollView's contentInset rather than resizing the frame for
fullscreen events.

Bug: none
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I70f2d814a15a24a6a0df3874565d8a41325a162a
Reviewed-on: https://chromium-review.googlesource.com/1009163
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Peter Lee <pkl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550085}

ios/chrome/browser/BUILD.gn

@@ -125,6 +125,7 @@ source_set("browser") {
     "//ios/chrome/browser/ui:feature_flags",
     "//ios/chrome/browser/ui/coordinators:chrome_coordinators",
     "//ios/chrome/browser/ui/external_search:features",
+    "//ios/chrome/browser/ui/fullscreen:features",
     "//ios/chrome/browser/ui/history:history_base_feature",
     "//ios/chrome/browser/ui/main:feature_flags",
     "//ios/chrome/browser/ui/omnibox",

ios/chrome/browser/about_flags.mm

@@ -46,6 +46,7 @@
 #include "ios/chrome/browser/mailto/features.h"
 #include "ios/chrome/browser/ssl/captive_portal_features.h"
 #include "ios/chrome/browser/ui/external_search/features.h"
+#import "ios/chrome/browser/ui/fullscreen/fullscreen_features.h"
 #import "ios/chrome/browser/ui/history/history_base_feature.h"
 #include "ios/chrome/browser/ui/main/main_feature_flags.h"
 #import "ios/chrome/browser/ui/popup_menu/popup_menu_flags.h"
@@ -266,6 +267,9 @@ const flags_ui::FeatureEntry kFeatureEntries[] = {
     {"ui-refresh-location-bar", flag_descriptions::kUIRefreshLocationBarName,
      flag_descriptions::kUIRefreshLocationBarDescription, flags_ui::kOsIos,
      FEATURE_VALUE_TYPE(kUIRefreshLocationBar)},
+    {"fullscreen-content-inset", flag_descriptions::kFullscreenContentInsetName,
+     flag_descriptions::kFullscreenContentInsetDescription, flags_ui::kOsIos,
+     FEATURE_VALUE_TYPE(fullscreen::features::kFullscreenContentInset)},
 };
 
 // Add all switches from experimental flags to |command_line|.

ios/chrome/browser/ios_chrome_flag_descriptions.cc

@@ -62,6 +62,12 @@ const char kFeedbackKitV2WithSSOServiceName[] =
 const char kFeedbackKitV2WithSSOServiceDescription[] =
     "Send SSOService with configuration for FeedbackKit V2.";
 
+const char kFullscreenContentInsetName[] = "Fullscreen ContentInset";
+const char kFullscreenContentInsetDescription[] =
+    "When enabled, fullscreen will be implemented by adjusting the "
+    "contentInset of the WKWebView's scroll view rather than adjusting its "
+    "frame.";
+
 const char kHistoryBatchUpdatesFilterName[] = "History Single Batch Filtering";
 const char kHistoryBatchUpdatesFilterDescription[] =
     "When enabled History inserts and deletes history items in the same "

ios/chrome/browser/ios_chrome_flag_descriptions.h

@@ -55,6 +55,11 @@ extern const char kFeedbackKitV2Description[];
 extern const char kFeedbackKitV2WithSSOServiceName[];
 extern const char kFeedbackKitV2WithSSOServiceDescription[];
 
+// Title and description for the flag used to enable fullscreen's contentInset
+// based implementation.
+extern const char kFullscreenContentInsetName[];
+extern const char kFullscreenContentInsetDescription[];
+
 // Title and description for the flag to enable History batch filtering.
 extern const char kHistoryBatchUpdatesFilterName[];
 extern const char kHistoryBatchUpdatesFilterDescription[];

ios/chrome/browser/ui/fullscreen/BUILD.gn

@@ -29,6 +29,19 @@ source_set("fullscreen") {
   ]
 }
 
+source_set("features") {
+  sources = [
+    "fullscreen_features.h",
+    "fullscreen_features.mm",
+  ]
+
+  configs += [ "//build/config/compiler:enable_arc" ]
+
+  deps = [
+    "//base",
+  ]
+}
+
 source_set("coordinators") {
   sources = [
     "chrome_coordinator+fullscreen_disabling.h",
@@ -70,6 +83,7 @@ source_set("internal") {
   configs += [ "//build/config/compiler:enable_arc" ]
 
   deps = [
+    ":features",
     ":ui",
     "//base",
     "//components/keyed_service/ios",

ios/chrome/browser/ui/fullscreen/fullscreen_features.h

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IOS_CHROME_BROWSER_UI_FULLSCREEN_FULLSCREEN_FEATURES_H_
+#define IOS_CHROME_BROWSER_UI_FULLSCREEN_FULLSCREEN_FEATURES_H_
+
+#include "base/feature_list.h"
+
+namespace fullscreen {
+namespace features {
+
+// Used to control whether fullscreen should be implemented by adjusting the
+// WKWebView's contentInset rather than its frame.
+extern const base::Feature kFullscreenContentInset;
+
+}  // namespace features
+}  // namespace fullscreen
+
+#endif  // IOS_CHROME_BROWSER_UI_FULLSCREEN_FULLSCREEN_FEATURES_H_

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

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/ui/fullscreen/fullscreen_features.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace fullscreen {
+namespace features {
+
+const base::Feature kFullscreenContentInset{"FullscreenContentInset",
+                                            base::FEATURE_DISABLED_BY_DEFAULT};
+
+}  // namespace features
+}  // namespace fullscreen

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

@@ -5,6 +5,7 @@
 #import "ios/chrome/browser/ui/fullscreen/fullscreen_web_state_observer.h"
 
 #include "base/logging.h"
+#import "ios/chrome/browser/ui/fullscreen/fullscreen_features.h"
 #import "ios/chrome/browser/ui/fullscreen/fullscreen_model.h"
 #import "ios/chrome/browser/ui/fullscreen/fullscreen_web_view_proxy_observer.h"
 #import "ios/chrome/browser/ui/fullscreen/scoped_fullscreen_disabler.h"
@@ -81,7 +82,10 @@ void FullscreenWebStateObserver::DidFinishNavigation(
   // - For normal pages, using |contentInset| breaks the layout of fixed-
   //   position DOM elements, so top padding must be accomplished by updating
   //   the WKWebView's frame.
+  bool force_content_inset = base::FeatureList::IsEnabled(
+      fullscreen::features::kFullscreenContentInset);
   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();