Display the stack view button only on iPhone

The stack view button is only needed on iPhone. The iPad have the tab
switcher button.

Bug: 791456
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Ie2f0044d59218d27f8253b3b44bea1c5fbc7ef19
Reviewed-on: https://chromium-review.googlesource.com/808864Reviewed-by: Elodie Banel <lod@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522063}

ios/chrome/browser/ui/toolbar/clean/toolbar_button.mm

@@ -50,7 +50,8 @@
     if (self.visibilityMask &
         ToolbarComponentVisibilityCompactWidthOnlyWhenEnabled) {
       newHiddenValue = !self.enabled;
-    } else if (self.visibilityMask & ToolbarComponentVisibilityCompactWidth) {
+    } else if (self.visibilityMask & ToolbarComponentVisibilityCompactWidth ||
+               self.visibilityMask & ToolbarComponentVisibilityIPhoneOnly) {
       newHiddenValue = NO;
     }
   } else {

ios/chrome/browser/ui/toolbar/clean/toolbar_component_options.h

@@ -20,6 +20,8 @@ typedef NS_OPTIONS(NSUInteger, ToolbarComponentVisibility) {
   // Use this option when the component should be visible in CompactWidth only
   // if it's enabled.
   ToolbarComponentVisibilityCompactWidthOnlyWhenEnabled = 1 << 2,
+  // Use this option when the component should be always visible on iPhone only.
+  ToolbarComponentVisibilityIPhoneOnly = 1 << 3,
 };
 
 #endif  // IOS_CHROME_BROWSER_UI_TOOLBAR_CLEAN_TOOLBAR_COMPONENT_OPTIONS_H_

ios/chrome/browser/ui/toolbar/clean/toolbar_view_controller.mm

@@ -389,8 +389,7 @@
   self.tabSwitchStripButton =
       [self.buttonFactory tabSwitcherStripToolbarButton];
   self.tabSwitchStripButton.visibilityMask =
-      ToolbarComponentVisibilityCompactWidth |
-      ToolbarComponentVisibilityRegularWidth;
+      ToolbarComponentVisibilityIPhoneOnly;
   [buttonConstraints
       addObject:[self.tabSwitchStripButton.widthAnchor
                     constraintEqualToConstant:kToolbarButtonWidth]];