[Mac] Fix hidden NSViews by bringing back a dedicated compositor view.

Until macOS 10.13, the relative ordering of a view's subviews' layers and
unassociated sublayers is undefined, so view layers can end up hidden behind
the compositor layer. See:

  https://developer.apple.com/library/archive/releasenotes/AppKit/RN-AppKit/index.html#10_13Layer-backed%20Views

This change re-adds a dedicated compositor view, but with less plumbing than
what was removed in r594160.

Bug: 865901, 899499
Change-Id: Ibbec83da2e8785e06522008dfc2d9eab7ca43bf9
Reviewed-on: https://chromium-review.googlesource.com/c/1334290
Commit-Queue: Sidney San Martín <sdy@chromium.org>
Reviewed-by: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608139}

ui/views/widget/native_widget_mac_unittest.mm

@@ -2206,11 +2206,8 @@ class NativeWidgetMacViewsOrderTest : public WidgetTest {
 
     widget_ = CreateTopLevelPlatformWidget();
 
-    // It's not a bug if the native view has a different number of subviews,
-    // but the rest of this test assumes it. It may or may not be worth
-    // removing that assumption at some point.
-    ASSERT_EQ(0u,
-              [[widget_->GetNativeView().GetNativeNSView() subviews] count]);
+    starting_subviews_.reset(
+        [[widget_->GetNativeView().GetNativeNSView() subviews] copy]);
 
     native_host_parent_ = new View();
     widget_->GetContentsView()->AddChildView(native_host_parent_);
@@ -2224,7 +2221,9 @@ class NativeWidgetMacViewsOrderTest : public WidgetTest {
     }
     EXPECT_EQ(kNativeViewCount, native_host_parent_->child_count());
     EXPECT_NSEQ([widget_->GetNativeView().GetNativeNSView() subviews],
-                (@[ hosts_[0]->view(), hosts_[1]->view(), hosts_[2]->view() ]));
+                ([GetStartingSubviews() arrayByAddingObjectsFromArray:@[
+                  hosts_[0]->view(), hosts_[1]->view(), hosts_[2]->view()
+                ]]));
   }
 
   void TearDown() override {
@@ -2236,9 +2235,12 @@ class NativeWidgetMacViewsOrderTest : public WidgetTest {
     return widget_->GetNativeView().GetNativeNSView();
   }
 
+  NSArray<NSView*>* GetStartingSubviews() { return starting_subviews_; }
+
   Widget* widget_ = nullptr;
   View* native_host_parent_ = nullptr;
   std::vector<std::unique_ptr<NativeHostHolder>> hosts_;
+  base::scoped_nsobject<NSArray<NSView*>> starting_subviews_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NativeWidgetMacViewsOrderTest);
@@ -2249,22 +2251,30 @@ class NativeWidgetMacViewsOrderTest : public WidgetTest {
 TEST_F(NativeWidgetMacViewsOrderTest, NativeViewAttached) {
   hosts_[1]->Detach();
   EXPECT_NSEQ([GetContentNativeView() subviews],
-              (@[ hosts_[0]->view(), hosts_[2]->view() ]));
+              ([GetStartingSubviews() arrayByAddingObjectsFromArray:@[
+                hosts_[0]->view(), hosts_[2]->view()
+              ]]));
 
   hosts_[1]->AttachNativeView();
   EXPECT_NSEQ([GetContentNativeView() subviews],
-              (@[ hosts_[0]->view(), hosts_[1]->view(), hosts_[2]->view() ]));
+              ([GetStartingSubviews() arrayByAddingObjectsFromArray:@[
+                hosts_[0]->view(), hosts_[1]->view(), hosts_[2]->view()
+              ]]));
 }
 
 // Tests that NativeViews order changes according to views::View hierarchy.
 TEST_F(NativeWidgetMacViewsOrderTest, ReorderViews) {
   native_host_parent_->ReorderChildView(hosts_[2]->host(), 1);
   EXPECT_NSEQ([GetContentNativeView() subviews],
-              (@[ hosts_[0]->view(), hosts_[2]->view(), hosts_[1]->view() ]));
+              ([GetStartingSubviews() arrayByAddingObjectsFromArray:@[
+                hosts_[0]->view(), hosts_[2]->view(), hosts_[1]->view()
+              ]]));
 
   native_host_parent_->RemoveChildView(hosts_[2]->host());
   EXPECT_NSEQ([GetContentNativeView() subviews],
-              (@[ hosts_[0]->view(), hosts_[1]->view() ]));
+              ([GetStartingSubviews() arrayByAddingObjectsFromArray:@[
+                hosts_[0]->view(), hosts_[1]->view()
+              ]]));
 
   View* new_parent = new View();
   native_host_parent_->RemoveChildView(hosts_[1]->host());
@@ -2272,11 +2282,15 @@ TEST_F(NativeWidgetMacViewsOrderTest, ReorderViews) {
   new_parent->AddChildView(hosts_[1]->host());
   new_parent->AddChildView(hosts_[2]->host());
   EXPECT_NSEQ([GetContentNativeView() subviews],
-              (@[ hosts_[0]->view(), hosts_[1]->view(), hosts_[2]->view() ]));
+              ([GetStartingSubviews() arrayByAddingObjectsFromArray:@[
+                hosts_[0]->view(), hosts_[1]->view(), hosts_[2]->view()
+              ]]));
 
   native_host_parent_->ReorderChildView(new_parent, 0);
   EXPECT_NSEQ([GetContentNativeView() subviews],
-              (@[ hosts_[1]->view(), hosts_[2]->view(), hosts_[0]->view() ]));
+              ([GetStartingSubviews() arrayByAddingObjectsFromArray:@[
+                hosts_[1]->view(), hosts_[2]->view(), hosts_[0]->view()
+              ]]));
 }
 
 // Test that unassociated native views stay on top after reordering.
@@ -2284,15 +2298,17 @@ TEST_F(NativeWidgetMacViewsOrderTest, UnassociatedViewsIsAbove) {
   base::scoped_nsobject<NSView> child_view([[NSView alloc] init]);
   [GetContentNativeView() addSubview:child_view];
   EXPECT_NSEQ(
-      [GetContentNativeView() subviews], (@[
+      [GetContentNativeView() subviews],
+      ([GetStartingSubviews() arrayByAddingObjectsFromArray:@[
         hosts_[0]->view(), hosts_[1]->view(), hosts_[2]->view(), child_view
-      ]));
+      ]]));
 
   native_host_parent_->ReorderChildView(hosts_[2]->host(), 1);
   EXPECT_NSEQ(
-      [GetContentNativeView() subviews], (@[
+      [GetContentNativeView() subviews],
+      ([GetStartingSubviews() arrayByAddingObjectsFromArray:@[
         hosts_[0]->view(), hosts_[2]->view(), hosts_[1]->view(), child_view
-      ]));
+      ]]));
 }
 
 // Test -[NSWindowDelegate windowShouldClose:].

ui/views_bridge_mac/bridged_native_widget_impl.mm

@@ -44,6 +44,18 @@ namespace {
 constexpr auto kUIPaintTimeout = base::TimeDelta::FromSeconds(5);
 }  // namespace
 
+// The NSView that hosts the composited CALayer drawing the UI. It fills the
+// window but is not hittable so that accessibility hit tests always go to the
+// BridgedContentView.
+@interface ViewsCompositorSuperview : NSView
+@end
+
+@implementation ViewsCompositorSuperview
+- (NSView*)hitTest:(NSPoint)aPoint {
+  return nil;
+}
+@end
+
 // Self-owning animation delegate that starts a hide animation, then calls
 // -[NSWindow close] when the animation ends, releasing itself.
 @interface ViewsNSWindowCloseAnimator : NSObject<NSAnimationDelegate> {
@@ -172,6 +184,9 @@ NSComparisonResult SubviewSorter(NSViewComparatorValue lhs,
                                  void* rank_as_void) {
   DCHECK_NE(lhs, rhs);
 
+  if ([lhs isKindOfClass:[ViewsCompositorSuperview class]])
+    return NSOrderedAscending;
+
   const RankMap* rank = static_cast<const RankMap*>(rank_as_void);
   auto left_rank = rank->find(lhs);
   auto right_rank = rank->find(rhs);
@@ -486,13 +501,20 @@ void BridgedNativeWidgetImpl::CreateContentView(uint64_t ns_view_id,
   // this should be treated as an error and caught early.
   CHECK(bridged_view_);
 
-  // Set the layer first to create a layer-hosting view (not layer-backed), and
-  // set the compositor output to go to that layer.
-  base::scoped_nsobject<CALayer> background_layer([[CALayer alloc] init]);
+  // Beware: This view was briefly removed (in favor of a bare CALayer) in
+  // crrev/c/1236675. The ordering of unassociated layers relative to NSView
+  // layers is undefined on macOS 10.12 and earlier, so the compositor layer
+  // ended up covering up subviews (see crbug/899499).
+  base::scoped_nsobject<NSView> compositor_view(
+      [[ViewsCompositorSuperview alloc] initWithFrame:[bridged_view_ bounds]]);
+  [compositor_view
+      setAutoresizingMask:NSViewWidthSizable | NSViewHeightSizable];
+  auto* background_layer = [CALayer layer];
   display_ca_layer_tree_ =
-      std::make_unique<ui::DisplayCALayerTree>(background_layer.get());
-  [bridged_view_ setLayer:background_layer];
-  [bridged_view_ setWantsLayer:YES];
+      std::make_unique<ui::DisplayCALayerTree>(background_layer);
+  [compositor_view setLayer:background_layer];
+  [compositor_view setWantsLayer:YES];
+  [bridged_view_ addSubview:compositor_view];
 
   [window_ setContentView:bridged_view_];
 }