FilesApp extension dialog: prevent resize cursor in tablet mode

In tablet mode, the extensions dialog has a fixed sized, and cannot be
resized. However, non-client hit testing in Ash calls canResize(), and
the current dialog code returns true: that causes Ash to show a resize
cursor on the non-client window edges of the dialog for mouse users.

Prevent that: when the dialog is active in Chrome OS tablet mode, deny
canResize() requests to stop the resize cursor appearing at the dialog
window edges.

Bug: 453634
Change-Id: I551e145c169c9844d3ac090a4e99d9eb826e6e5a
Reviewed-on: https://chromium-review.googlesource.com/c/1280383Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Ben Wells <benwells@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599807}

chrome/browser/ui/views/extensions/extension_dialog.cc

@@ -25,6 +25,10 @@
 #include "ui/views/widget/widget.h"
 #include "url/gurl.h"
 
+#if defined(OS_CHROMEOS)
+#include "chrome/browser/ui/ash/tablet_mode_client.h"
+#endif
+
 using content::BrowserContext;
 using content::WebContents;
 
@@ -153,6 +157,12 @@ int ExtensionDialog::GetDialogButtons() const {
 }
 
 bool ExtensionDialog::CanResize() const {
+#if defined(OS_CHROMEOS)
+  // Prevent dialog resize mouse cursor in tablet mode, crbug.com/453634.
+  const auto* client = TabletModeClient::Get();
+  if (client && client->tablet_mode_enabled())
+    return false;
+#endif
   // Can resize only if minimum contents size set.
   return GetExtensionView()->GetPreferredSize() != gfx::Size();
 }