Remove restore button in tablet mode on Windows.

Tablet mode has no restore functionality since all windows are
effectively "maximized" even in split-screen mode.

Bug: 1111019
Change-Id: I397c6a66cc9c337d0bb8e04e33bf8e4a44153d2e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2327645Reviewed-by: Collin Baker <collinbaker@chromium.org>
Commit-Queue: Dana Fried <dfried@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792917}

chrome/browser/ui/views/frame/glass_browser_caption_button_container.cc

@@ -107,8 +107,15 @@ void GlassBrowserCaptionButtonContainer::OnWidgetBoundsChanged(
 }
 
 void GlassBrowserCaptionButtonContainer::UpdateButtonVisibility() {
-  const bool is_maximized = frame_view_->IsMaximized();
-  restore_button_->SetVisible(is_maximized);
-  maximize_button_->SetVisible(!is_maximized);
+  if (frame_view_->IsWebUITabStrip()) {
+    // In tablet mode, all windows are effectively full-screen and cannot be
+    // restored, so don't show either button.
+    restore_button_->SetVisible(false);
+    maximize_button_->SetVisible(false);
+  } else {
+    const bool is_maximized = frame_view_->IsMaximized();
+    restore_button_->SetVisible(is_maximized);
+    maximize_button_->SetVisible(!is_maximized);
+  }
   InvalidateLayout();
 }

chrome/browser/ui/views/frame/glass_browser_frame_view.cc

@@ -389,6 +389,11 @@ bool GlassBrowserFrameView::IsMaximized() const {
   return frame()->IsMaximized();
 }
 
+bool GlassBrowserFrameView::IsWebUITabStrip() const {
+  return WebUITabStripContainerView::UseTouchableTabStrip(
+      browser_view()->browser());
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // GlassBrowserFrameView, views::View overrides:
 
@@ -552,11 +557,6 @@ bool GlassBrowserFrameView::ShowSystemIcon() const {
          browser_view()->ShouldShowWindowIcon();
 }
 
-bool GlassBrowserFrameView::IsWebUITabStrip() const {
-  return WebUITabStripContainerView::UseTouchableTabStrip(
-      browser_view()->browser());
-}
-
 bool GlassBrowserFrameView::OwnsCaptionButtons() const {
   return caption_button_container_ &&
          caption_button_container_->parent() == this;

chrome/browser/ui/views/frame/glass_browser_frame_view.h

@@ -66,6 +66,7 @@ class GlassBrowserFrameView : public BrowserNonClientFrameView,
   gfx::ImageSkia GetFaviconForTabIconView() override;
 
   bool IsMaximized() const;
+  bool IsWebUITabStrip() const;
 
   // Visual height of the titlebar when the window is maximized (i.e. excluding
   // the area above the top of the screen).
@@ -122,7 +123,6 @@ class GlassBrowserFrameView : public BrowserNonClientFrameView,
   bool ShowCustomIcon() const;
   bool ShowCustomTitle() const;
   bool ShowSystemIcon() const;
-  bool IsWebUITabStrip() const;
 
   // Returns true if caption buttons are present on the frame (as opposed to
   // somewhere else, or not present at all). In some modes, the frame can "lend"