Add test-only hook to get a callback when dragging enters a target view.

This will be used by drag and drop tests to take action on dragging over various
views (typically, sending a mouse release event to end the drag).

Bug: 923188
Change-Id: I40a3885cf8076f9e0a5f0490ca1eda3f32907086
Reviewed-on: https://chromium-review.googlesource.com/c/1493435
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636343}

ui/views/widget/drop_helper.cc

@@ -4,6 +4,8 @@
 
 #include "ui/views/widget/drop_helper.h"
 
+#include "base/callback.h"
+#include "base/no_destructor.h"
 #include "build/build_config.h"
 #include "ui/base/dragdrop/drag_drop_types.h"
 #include "ui/views/view.h"
@@ -11,6 +13,17 @@
 
 namespace views {
 
+namespace {
+
+const View* g_drag_entered_callback_view = nullptr;
+
+base::RepeatingClosure* GetDragEnteredCallback() {
+  static base::NoDestructor<base::RepeatingClosure> callback;
+  return callback.get();
+}
+
+}  // namespace
+
 DropHelper::DropHelper(View* root_view)
     : root_view_(root_view),
       target_view_(NULL),
@@ -20,6 +33,14 @@ DropHelper::DropHelper(View* root_view)
 DropHelper::~DropHelper() {
 }
 
+// static
+void DropHelper::SetDragEnteredCallbackForTesting(
+    const View* view,
+    base::RepeatingClosure callback) {
+  g_drag_entered_callback_view = view;
+  *GetDragEnteredCallback() = std::move(callback);
+}
+
 void DropHelper::ResetTargetViewIfEquals(View* view) {
   if (target_view_ == view)
     target_view_ = NULL;
@@ -30,16 +51,26 @@ void DropHelper::ResetTargetViewIfEquals(View* view) {
 int DropHelper::OnDragOver(const OSExchangeData& data,
                            const gfx::Point& root_view_location,
                            int drag_operation) {
+  const View* old_deepest_view = deepest_view_;
   View* view = CalculateTargetViewImpl(root_view_location, data, true,
                                        &deepest_view_);
 
   if (view != target_view_) {
-    // Target changed notify old drag exited, then new drag entered.
+    // Target changed. Notify old drag exited, then new drag entered.
     NotifyDragExit();
     target_view_ = view;
     NotifyDragEntered(data, root_view_location, drag_operation);
   }
 
+  // Notify testing callback if the drag newly moved over the target view.
+  if (g_drag_entered_callback_view &&
+      g_drag_entered_callback_view->Contains(deepest_view_) &&
+      !g_drag_entered_callback_view->Contains(old_deepest_view)) {
+    auto* callback = GetDragEnteredCallback();
+    if (!callback->is_null())
+      callback->Run();
+  }
+
   return NotifyDragOver(data, root_view_location, drag_operation);
 }
 

ui/views/widget/drop_helper.h

@@ -5,8 +5,10 @@
 #ifndef UI_VIEWS_WIDGET_DROP_HELPER_H_
 #define UI_VIEWS_WIDGET_DROP_HELPER_H_
 
-#include "base/macros.h"
+#include <utility>
 
+#include "base/callback_forward.h"
+#include "base/macros.h"
 #include "ui/views/views_export.h"
 
 namespace gfx {
@@ -33,6 +35,11 @@ class VIEWS_EXPORT DropHelper {
   explicit DropHelper(View* root_view);
   ~DropHelper();
 
+  // Sets a callback that is run any time a drag enters |view|.  Only exposed
+  // for testing.
+  static void SetDragEnteredCallbackForTesting(const View* view,
+                                               base::RepeatingClosure callback);
+
   // Current view drop events are targeted at, may be NULL.
   View* target_view() const { return target_view_; }