Revert "[iOS] Set FirstResponderSendAction as default"

This reverts commit 2aa1a2f6.

Reason for revert: Potential culprit for crbug.com/1152587

Original change's description:
> [iOS] Set FirstResponderSendAction as default
>
> Remove experiment flag, and set enabled behavior as default.
>
> Keep old behavior when asking the NTP and WebView to become first
> responder. This is done checking if the first responder is a view, and
> asking if not. Because in the previous logic for GetFirstResponder() the
> search was made in the view hierarchy, ignoring view controllers.
>
> The experiment enabled without the check added in this CL could explain
> issues like crbug.com/1150498.
>
> Bug: 816427, 1150498
> Change-Id: Ib9ac17b59da8635d00beff071aee4bd6afeedb78
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495976
> Reviewed-by: Gauthier Ambard <gambard@chromium.org>
> Commit-Queue: Javier Flores <javierrobles@chromium.org>
> Auto-Submit: Javier Flores <javierrobles@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#830632}

TBR=gambard@chromium.org,javierrobles@chromium.org

Change-Id: If4c1451b7ed278b02164f0816d8b01bf11314289
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 816427
Bug: 1150498
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2560097Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830927}

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

@@ -3772,12 +3772,9 @@ NSString* const kBrowserViewControllerSnackbarCategory =
     [SizeClassRecorder pageLoadedWithHorizontalSizeClass:sizeClass];
   }
 
-  // If there is no first responder, or it is not a view, try to make the
-  // webview or the NTP first responder to have it answer keyboard commands
-  // (e.g. space bar to scroll).
-  BOOL isFirstResponderView =
-      [GetFirstResponder() isKindOfClass:[UIView class]];
-  if (!isFirstResponderView && self.currentWebState) {
+  // If there is no first responder, try to make the webview or the NTP first
+  // responder to have it answer keyboard commands (e.g. space bar to scroll).
+  if (!GetFirstResponder() && self.currentWebState) {
     NewTabPageTabHelper* NTPHelper =
         NewTabPageTabHelper::FromWebState(webState);
     if (NTPHelper && NTPHelper->IsActive()) {

ios/chrome/browser/ui/ui_feature_flags.cc

@@ -31,6 +31,9 @@ const base::Feature kForceUnstackedTabstrip{"ForceUnstackedTabstrip",
 const base::Feature kTestFeature{"TestFeature",
                                  base::FEATURE_DISABLED_BY_DEFAULT};
 
+const base::Feature kFirstResponderSendAction{
+    "FirstResponderSendAction", base::FEATURE_DISABLED_BY_DEFAULT};
+
 const base::Feature kEnableNativeContextMenus{
     "EnableNativeContextMenus", base::FEATURE_DISABLED_BY_DEFAULT};
 

ios/chrome/browser/ui/ui_feature_flags.h

@@ -34,6 +34,9 @@ extern const base::Feature kForceUnstackedTabstrip;
 // features in tests works.
 extern const base::Feature kTestFeature;
 
+// Verify if the crash in https://crbug.com/816427 is fixed on iOS 12.
+extern const base::Feature kFirstResponderSendAction;
+
 // Feature flag that enables the native UI Context Menus (not for Web content).
 extern const base::Feature kEnableNativeContextMenus;
 

ios/chrome/browser/ui/util/uikit_ui_util.h

@@ -181,7 +181,7 @@ bool IsSplitToolbarMode(id<UITraitEnvironment> environment);
 // bottom toolbar or if it is displayed as only one toolbar.
 bool IsSplitToolbarMode(UITraitCollection* traitCollection);
 
-// Returns the current first responder.
+// Returns the current first responder for keyWindow.
 UIResponder* GetFirstResponder();
 
 // Trigger a haptic vibration for various types of actions. This is a no-op for

ios/chrome/browser/ui/util/uikit_ui_util.mm

@@ -315,15 +315,19 @@ UIView* GetFirstResponderSubview(UIView* view) {
 
 UIResponder* GetFirstResponder() {
   DCHECK_CURRENTLY_ON(web::WebThread::UI);
-  DCHECK(!g_first_responder);
-  [[UIApplication sharedApplication]
-      sendAction:@selector(cr_markSelfCurrentFirstResponder)
-              to:nil
-            from:nil
-        forEvent:nil];
-  UIResponder* firstResponder = g_first_responder;
-  g_first_responder = nil;
-  return firstResponder;
+  if (base::FeatureList::IsEnabled(kFirstResponderSendAction)) {
+    DCHECK_CURRENTLY_ON(web::WebThread::UI);
+    DCHECK(!g_first_responder);
+    [[UIApplication sharedApplication]
+        sendAction:@selector(cr_markSelfCurrentFirstResponder)
+                to:nil
+              from:nil
+          forEvent:nil];
+    UIResponder* firstResponder = g_first_responder;
+    g_first_responder = nil;
+    return firstResponder;
+  }
+  return GetFirstResponderSubview([UIApplication sharedApplication].keyWindow);
 }
 
 // Trigger a haptic vibration for the user selecting an action. This is a no-op