views: have WidgetDelegate update widget size constraints

Currently clients of the SetCan{Maximize,Minimize,Resize} setters need
to remember to call Widget::OnSizeConstraintsChanged afterwards, which
is obviously dangerous. Just call it from inside the setters, and
then we can stop calling it everywhere else. OnSizeConstraintsChanged
is idempotent (though a bit expensive) so temporarily having two calls
to it won't hurt anything.

This change also fixes ViewEventTestBase::GetWidget() to tolerate
being called early in the object's lifecycle.

Bug: 1075649
Change-Id: I11dcf39e6b1ad86f8d5f5adfa973e5fd339dd36f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485195
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819017}

chrome/browser/ui/views/test/view_event_test_base.cc

@@ -66,9 +66,11 @@ class TestBaseWidgetDelegate : public views::WidgetDelegate {
 
   // views::WidgetDelegate:
   void WindowClosing() override { harness_->window_ = nullptr; }
-  views::Widget* GetWidget() override { return contents_->GetWidget(); }
+  views::Widget* GetWidget() override {
+    return contents_ ? contents_->GetWidget() : nullptr;
+  }
   const views::Widget* GetWidget() const override {
-    return contents_->GetWidget();
+    return contents_ ? contents_->GetWidget() : nullptr;
   }
   views::View* GetContentsView() override {
     // This will first be called by Widget::Init(), which passes the returned

ui/views/widget/widget_delegate.cc

@@ -251,15 +251,21 @@ void WidgetDelegate::SetAccessibleTitle(base::string16 title) {
 }
 
 void WidgetDelegate::SetCanMaximize(bool can_maximize) {
-  params_.can_maximize = can_maximize;
+  std::exchange(params_.can_maximize, can_maximize);
+  if (GetWidget() && params_.can_maximize != can_maximize)
+    GetWidget()->OnSizeConstraintsChanged();
 }
 
 void WidgetDelegate::SetCanMinimize(bool can_minimize) {
-  params_.can_minimize = can_minimize;
+  std::exchange(params_.can_minimize, can_minimize);
+  if (GetWidget() && params_.can_minimize != can_minimize)
+    GetWidget()->OnSizeConstraintsChanged();
 }
 
 void WidgetDelegate::SetCanResize(bool can_resize) {
-  params_.can_resize = can_resize;
+  std::exchange(params_.can_resize, can_resize);
+  if (GetWidget() && params_.can_resize != can_resize)
+    GetWidget()->OnSizeConstraintsChanged();
 }
 
 void WidgetDelegate::SetOwnedByWidget(bool owned) {