[ios] Add Browser-scoped FullscreenController flag

This flag will be used to build out support for scoping FullscreenController
to a Browser while keeping the current BrowserState-scoped logic as default.

Bug: 790886
Change-Id: Iac1811181a6313271561ffecae306fe4b7b94684
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2007314
Commit-Queue: Chris Lu <thegreenfrog@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734534}

ios/chrome/browser/flags/about_flags.mm

@@ -601,6 +601,12 @@ const flags_ui::FeatureEntry kFeatureEntries[] = {
      flag_descriptions::kChangeTabSwitcherPositionName,
      flag_descriptions::kChangeTabSwitcherPositionDescription, flags_ui::kOsIos,
      FEATURE_VALUE_TYPE(kChangeTabSwitcherPosition)},
+    {"fullscreen-controller-browser-scoped",
+     flag_descriptions::kFullscreenControllerBrowserScopedName,
+     flag_descriptions::kFullscreenControllerBrowserScopedDescription,
+     flags_ui::kOsIos,
+     FEATURE_VALUE_TYPE(
+         fullscreen::features::kFullscreenControllerBrowserScoped)},
 };
 
 // Add all switches from experimental flags to |command_line|.

ios/chrome/browser/flags/ios_chrome_flag_descriptions.cc

@@ -245,6 +245,12 @@ const char kFullscreenSmoothScrollingDescription[] =
     "When enabled, the web view's insets are updated for scoll events. If "
     "disabled, the the web view's frame are updated.";
 
+const char kFullscreenControllerBrowserScopedName[] =
+    "Scope FullscreenController to Browser";
+const char kFullscreenControllerBrowserScopedDescription[] =
+    "When enabled, FullscreenController will be stored and retrieved using the "
+    "Browser.";
+
 const char kIgnoresViewportScaleLimitsName[] = "Ignore Viewport Scale Limits";
 const char kIgnoresViewportScaleLimitsDescription[] =
     "When enabled the page can always be scaled, regardless of author intent.";

ios/chrome/browser/flags/ios_chrome_flag_descriptions.h

@@ -209,6 +209,11 @@ extern const char kForceUnstackedTabstripDescription[];
 extern const char kFullscreenSmoothScrollingName[];
 extern const char kFullscreenSmoothScrollingDescription[];
 
+// Title and description for the flag to scope FullscreenController to a
+// Browser.
+extern const char kFullscreenControllerBrowserScopedName[];
+extern const char kFullscreenControllerBrowserScopedDescription[];
+
 // Title and description for the flag to ignore viewport scale limits.
 extern const char kIgnoresViewportScaleLimitsName[];
 extern const char kIgnoresViewportScaleLimitsDescription[];

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

@@ -15,10 +15,17 @@ namespace features {
 // viewport adjustment experiment is selected via command line switches.
 extern const base::Feature kSmoothScrollingDefault;
 
+// Feature used to enable scoping FullscreenController to a Browser.
+extern const base::Feature kFullscreenControllerBrowserScoped;
+
 // Convenience method for determining when to adjust the viewport by resizing
 // WKWebView or using smooth scrolling.
 bool ShouldUseSmoothScrolling();
 
+// Convenience method for determining when FullscreenController is stored and
+// retrieved using the Browser instead of the BrowserState.
+bool ShouldScopeFullscreenControllerToBrowser();
+
 }  // namespace features
 }  // namespace fullscreen
 

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

@@ -17,9 +17,16 @@ namespace features {
 const base::Feature kSmoothScrollingDefault{"FullscreenSmoothScrollingDefault",
                                             base::FEATURE_ENABLED_BY_DEFAULT};
 
+const base::Feature kFullscreenControllerBrowserScoped{
+    "FullscreenControllerBrowserScoped", base::FEATURE_DISABLED_BY_DEFAULT};
+
 bool ShouldUseSmoothScrolling() {
   return base::FeatureList::IsEnabled(kSmoothScrollingDefault);
 }
 
+bool ShouldScopeFullscreenControllerToBrowser() {
+  return base::FeatureList::IsEnabled(kFullscreenControllerBrowserScoped);
+}
+
 }  // namespace features
 }  // namespace fullscreen