Reland "Remove unneeded CursorLoaderWin::SetPlatformWindow calls"

This is a reland of 1208732e

Original change's description:
> Remove unneeded CursorLoaderWin::SetPlatformWindow calls
>
> SetCursorNative is only called from WindowTreeHost::SetCursor, which
> guarantees that the platform cursor has been set.
>
> Bug: 1097556
> Change-Id: I4c140a872482ba33bf957ed6817279c275bf7f36
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417893
> Reviewed-by: Scott Violet <sky@chromium.org>
> Commit-Queue: Henrique Ferreiro <hferreiro@igalia.com>
> Cr-Commit-Position: refs/heads/master@{#810120}

Bug: 1097556
Change-Id: I89b742a80ddd9fee7a77b5af1bee07b58c18f39b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2445550Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Henrique Ferreiro <hferreiro@igalia.com>
Cr-Commit-Position: refs/heads/master@{#837132}

ui/aura/window_tree_host.cc

@@ -219,6 +219,10 @@ void WindowTreeHost::ConvertPixelsToDIP(gfx::Point* point) const {
 }
 
 void WindowTreeHost::SetCursor(gfx::NativeCursor cursor) {
+  // Some CursorFactory implementations use nullptr to represent the hidden
+  // cursor (i.e. cursor type kNone).
+  DCHECK(cursor.type() == ui::mojom::CursorType::kNone || cursor.platform());
+
   last_cursor_ = cursor;
   // A lot of code seems to depend on NULL cursors actually showing an arrow,
   // so just pass everything along to the host.

ui/aura/window_tree_host.h

@@ -136,11 +136,12 @@ class AURA_EXPORT WindowTreeHost : public ui::internal::InputMethodDelegate,
   // root window's.
   virtual void ConvertPixelsToDIP(gfx::Point* point) const;
 
-  // Cursor.
   // Sets the currently-displayed cursor. If the cursor was previously hidden
   // via ShowCursor(false), it will remain hidden until ShowCursor(true) is
   // called, at which point the cursor that was last set via SetCursor() will be
   // used.
+  // `cursor` should have its platform cursor set, e.g. via
+  // `CursorLoader::SetPlatformCursor`.
   void SetCursor(gfx::NativeCursor cursor);
 
   // Invoked when the cursor's visibility has changed.

ui/aura/window_tree_host_platform.cc

@@ -34,7 +34,6 @@
 #endif
 
 #if defined(OS_WIN)
-#include "ui/base/cursor/cursor_loader_win.h"
 #include "ui/platform_window/win/win_window.h"
 #endif
 
@@ -185,11 +184,6 @@ void WindowTreeHostPlatform::SetCursorNative(gfx::NativeCursor cursor) {
     return;
   current_cursor_ = cursor;
 
-#if defined(OS_WIN)
-  ui::CursorLoaderWin cursor_loader;
-  cursor_loader.SetPlatformCursor(&cursor);
-#endif
-
   platform_window_->SetCursor(cursor.platform());
 }
 

ui/base/cursor/cursor_loader_win.cc

@@ -160,6 +160,8 @@ void CursorLoaderWin::SetPlatformCursor(gfx::NativeCursor* cursor) {
           GetModuleHandle(g_cursor_resource_module_name.Get().c_str()),
           cursor_id);
     }
+    DCHECK(platform_cursor)
+        << "Failed to load a cursor for type " << cursor->type();
     cursor->SetPlatformCursor(platform_cursor);
   }
 }

ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc

@@ -22,7 +22,6 @@
 #include "ui/aura/client/focus_client.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/base/class_property.h"
-#include "ui/base/cursor/cursor_loader_win.h"
 #include "ui/base/ime/input_method.h"
 #include "ui/base/ui_base_features.h"
 #include "ui/base/win/event_creation_utils.h"
@@ -632,9 +631,6 @@ DesktopWindowTreeHostWin::GetKeyboardLayoutMap() {
 void DesktopWindowTreeHostWin::SetCursorNative(gfx::NativeCursor cursor) {
   TRACE_EVENT1("ui,input", "DesktopWindowTreeHostWin::SetCursorNative",
                "cursor", cursor.type());
-  ui::CursorLoaderWin cursor_loader;
-  cursor_loader.SetPlatformCursor(&cursor);
-
   message_handler_->SetCursor(cursor.platform());
 }