[iOS] Add flag to disable hiding the bottom toolbar for fullscreen.

Bug: 961449
Change-Id: Ia45b11b8976f4fa7fb98bb4cd7451d2737027365
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1603525Reviewed-by: Peter Lee <pkl@chromium.org>
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658300}

ios/chrome/browser/about_flags.mm

@@ -583,6 +583,9 @@ const flags_ui::FeatureEntry kFeatureEntries[] = {
     {"language-settings", flag_descriptions::kLanguageSettingsName,
      flag_descriptions::kLanguageSettingsDescription, flags_ui::kOsIos,
      FEATURE_VALUE_TYPE(kLanguageSettings)},
+    {"lock-bottom-toolbar", flag_descriptions::kLockBottomToolbarName,
+     flag_descriptions::kLockBottomToolbarDescription, flags_ui::kOsIos,
+     FEATURE_VALUE_TYPE(fullscreen::features::kLockBottomToolbar)},
 };
 
 // Add all switches from experimental flags to |command_line|.

ios/chrome/browser/ios_chrome_flag_descriptions.cc

@@ -294,6 +294,11 @@ const char kLanguageSettingsDescription[] =
     "Enables the Language Settings page allowing modifications to user "
     "preferred languages and translate preferences.";
 
+const char kLockBottomToolbarName[] = "Lock bottom toolbar";
+const char kLockBottomToolbarDescription[] =
+    "When enabled, the bottom toolbar will not get collapsed when scrolling "
+    "into fullscreen mode.";
+
 const char kMarkHttpAsName[] = "Mark non-secure origins as non-secure";
 const char kMarkHttpAsDescription[] = "Change the UI treatment for HTTP pages";
 

ios/chrome/browser/ios_chrome_flag_descriptions.h

@@ -240,6 +240,10 @@ extern const char kInProductHelpDemoModeDescription[];
 extern const char kLanguageSettingsName[];
 extern const char kLanguageSettingsDescription[];
 
+// Title and description for the flag to lock the bottom toolbar into place.
+extern const char kLockBottomToolbarName[];
+extern const char kLockBottomToolbarDescription[];
+
 // Title, description, and options for the MarkHttpAs setting that controls
 // display of omnibox warnings about non-secure pages.
 extern const char kMarkHttpAsName[];

ios/chrome/browser/ui/browser_view/browser_view_controller.mm

@@ -3749,6 +3749,10 @@ NSString* const kBrowserViewControllerSnackbarCategory =
 // Translates the footer view up and down according to |progress|, where a
 // progress of 1.0 fully shows the footer and a progress of 0.0 fully hides it.
 - (void)updateFootersForFullscreenProgress:(CGFloat)progress {
+  // If the bottom toolbar is locked into place, reset |progress| to 1.0.
+  if (base::FeatureList::IsEnabled(fullscreen::features::kLockBottomToolbar))
+    progress = 1.0;
+
   self.footerFullscreenProgress = progress;
 
   CGFloat height = 0.0;
@@ -3790,8 +3794,13 @@ NSString* const kBrowserViewControllerSnackbarCategory =
   // safe area, so the unsafe top height must be added.
   CGFloat top = AlignValueToPixel(
       self.headerHeight + (progress - 1.0) * [self nonFullscreenToolbarHeight]);
-  CGFloat bottom =
-      AlignValueToPixel(progress * [self secondaryToolbarHeightWithInset]);
+  // If the bottom toolbar is locked into place, use 1.0 instead of |progress|.
+  CGFloat bottomProgress =
+      base::FeatureList::IsEnabled(fullscreen::features::kLockBottomToolbar)
+          ? 1.0
+          : progress;
+  CGFloat bottom = AlignValueToPixel(bottomProgress *
+                                     [self secondaryToolbarHeightWithInset]);
 
   if (self.usesSafeInsetsForViewportAdjustments) {
     if (fullscreen::features::GetActiveViewportExperiment() ==

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

@@ -5,6 +5,7 @@
 #ifndef IOS_CHROME_BROWSER_UI_FULLSCREEN_FULLSCREEN_FEATURES_H_
 #define IOS_CHROME_BROWSER_UI_FULLSCREEN_FULLSCREEN_FEATURES_H_
 
+#include "base/feature_list.h"
 #include "components/flags_ui/feature_entry.h"
 
 namespace fullscreen {
@@ -36,6 +37,10 @@ enum class ViewportAdjustmentExperiment : short {
 // from the command line.
 ViewportAdjustmentExperiment GetActiveViewportExperiment();
 
+// Used to control whether the bottom toolbar should be locked into the extended
+// position (i.e. fullscreen progress == 1.0).
+extern const base::Feature kLockBottomToolbar;
+
 }  // namespace features
 }  // namespace fullscreen
 

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

@@ -66,5 +66,8 @@ ViewportAdjustmentExperiment GetActiveViewportExperiment() {
              : ViewportAdjustmentExperiment::FRAME;
 }
 
+const base::Feature kLockBottomToolbar{"LockBottomToolbar",
+                                       base::FEATURE_DISABLED_BY_DEFAULT};
+
 }  // namespace features
 }  // namespace fullscreen

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

@@ -11,6 +11,7 @@
 #include "base/macros.h"
 #include "base/observer_list.h"
 #import "ios/chrome/browser/ui/broadcaster/chrome_broadcast_observer_bridge.h"
+#import "ios/chrome/browser/ui/fullscreen/fullscreen_features.h"
 #import "ios/chrome/browser/ui/fullscreen/scoped_fullscreen_disabler.h"
 
 class FullscreenModelObserver;
@@ -72,10 +73,14 @@ class FullscreenModel : public ChromeBroadcastObserverInterface {
 
   // Returns the toolbar insets at |progress|.
   UIEdgeInsets GetToolbarInsetsAtProgress(CGFloat progress) const {
+    const CGFloat kBottomToolbarProgress =
+        base::FeatureList::IsEnabled(fullscreen::features::kLockBottomToolbar)
+            ? 1.0
+            : progress;
     return UIEdgeInsetsMake(
         collapsed_toolbar_height_ +
             progress * (expanded_toolbar_height_ - collapsed_toolbar_height_),
-        0, progress * bottom_toolbar_height_, 0);
+        0, kBottomToolbarProgress * bottom_toolbar_height_, 0);
   }
 
   // Increments and decrements |disabled_counter_| for features that require the