Add a new SetContentsView API to accept unique_ptr

Since the majority of use cases is to let Widget to own its content
view, and we are moving towards removing those cases otherwise, this CL
adds a new API to make the ownership transfer clearer. In the
followup CL, we should move most of current use cases to adopt
this new API.

BUG=1044687

Change-Id: Ie21fd78cda1c74252171d543f1840405b8d48a10
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2198363Reviewed-by: Robert Liao <robliao@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Wei Li <weili@chromium.org>
Cr-Commit-Position: refs/heads/master@{#768877}

ui/views/widget/widget.h

@@ -497,7 +497,18 @@ class VIEWS_EXPORT Widget : public internal::NativeWidgetDelegate,
   // Sets the specified view as the contents of this Widget. There can only
   // be one contents view child of this Widget's RootView. This view is sized to
   // fit the entire size of the RootView. The RootView takes ownership of this
-  // View, unless it is set as not being parent-owned.
+  // View, unless it is passed in as a raw pointer and set as not being
+  // parent-owned. Prefer using SetContentsView(std::unique_ptr) over passing a
+  // raw pointer for new code.
+  template <typename T>
+  T* SetContentsView(std::unique_ptr<T> view) {
+    DCHECK(!view->owned_by_client())
+        << "This should only be called if the client is passing over the "
+           "ownership of |view|.";
+    T* raw_pointer = view.get();
+    SetContentsView(view.release());
+    return raw_pointer;
+  }
   void SetContentsView(View* view);
 
   // NOTE: This may not be the same view as WidgetDelegate::GetContentsView().

ui/views/widget/widget_unittest.cc

@@ -1333,9 +1333,8 @@ class DesktopAuraPaintWidgetTest : public DesktopWidgetTest {
         CreateParamsForTestWidget(type));
     paint_widget_ = widget.get();
 
-    View* contents_view = new View();
+    View* contents_view = widget->SetContentsView(std::make_unique<View>());
     contents_view->SetFocusBehavior(View::FocusBehavior::ALWAYS);
-    widget->SetContentsView(contents_view);
 
     widget->Show();
     widget->Activate();
@@ -2009,7 +2008,8 @@ TEST_F(WidgetTest, WidgetDeleted_InOnMousePressed) {
       CreateParams(views::Widget::InitParams::TYPE_POPUP);
   widget->Init(std::move(params));
 
-  widget->SetContentsView(new CloseWidgetView(ui::ET_MOUSE_PRESSED));
+  widget->SetContentsView(
+      std::make_unique<CloseWidgetView>(ui::ET_MOUSE_PRESSED));
 
   widget->SetSize(gfx::Size(100, 100));
   widget->Show();
@@ -2034,7 +2034,8 @@ TEST_F(WidgetTest, WidgetDeleted_InDispatchGestureEvent) {
       CreateParams(views::Widget::InitParams::TYPE_POPUP);
   widget->Init(std::move(params));
 
-  widget->SetContentsView(new CloseWidgetView(ui::ET_GESTURE_TAP_DOWN));
+  widget->SetContentsView(
+      std::make_unique<CloseWidgetView>(ui::ET_GESTURE_TAP_DOWN));
 
   widget->SetSize(gfx::Size(100, 100));
   widget->Show();