MacViews: Fix crash due to failed DCHECK in BridgedNativeWidget.

ui/views/cocoa/bridged_native_widget.mm

Index: ui/views/cocoa/bridged_native_widget.mm
diff --git a/ui/views/cocoa/bridged_native_widget.mm b/ui/views/cocoa/bridged_native_widget.mm
index b0ab01429cdce334feb89a25766c3dd61b38532a..9acc7f3f1abd8b705e699bfa1d180d271ef5bb56 100644
--- a/ui/views/cocoa/bridged_native_widget.mm
+++ b/ui/views/cocoa/bridged_native_widget.mm
@@ -312,6 +312,19 @@ NSComparisonResult SubviewSorter(NSViewComparatorValue lhs,
   return NSOrderedSame;
 }
 
+#if DCHECK_IS_ON()

[tapted, 2016/10/06 07:38:46]

dang it - typically this is required to avoid a "this is unused" warning (which
also only shows up once you get run on a bot that doesn't have DCHECKs :/). But
I guess we can just try without. So, lgtm with this #if removed as well :) (but
perhaps worth just building a is_debug = false build without DCHECKs to ensure
that's the case)

[karandeepb, 2016/10/07 01:03:57]

Yeah, so the arguments to the DCHECK macros are still compiled in, but not used
on RELEASE builds, which caused the failure.

+// Counts windows managed by a BridgedNativeWidget instance in the
+// |child_windows| array ignoring the windows added by AppKit.
+NSUInteger CountBridgedWindows(NSArray* child_windows) {
+  NSUInteger count = 0;
+  for (NSWindow* child in child_windows)
+    if ([[child delegate] isKindOfClass:[ViewsNSWindowDelegate class]])
+      ++count;
+
+  return count;
+}
+#endif
+
 }  // namespace
 
 namespace views {
@@ -1190,19 +1203,21 @@ NSComparisonResult SubviewSorter(NSViewComparatorValue lhs,
     // The orderOut calls above should result in a call to OnVisibilityChanged()
     // in each child. There, children will remove themselves from the NSWindow
     // childWindow list as well as propagate NotifyVisibilityChangeDown() calls
-    // to any children of their own.
-    DCHECK_EQ(0u, [[window_ childWindows] count]);
+    // to any children of their own. However this is only true for windows
+    // managed by the BridgedNativeWidget i.e. windows which have
+    // ViewsNSWindowDelegate as the delegate.
+    DCHECK_EQ(0u, CountBridgedWindows([window_ childWindows]));
     return;
   }
 
-  NSUInteger visible_children = 0;  // For a DCHECK below.
+  NSUInteger visible_bridged_children = 0;  // For a DCHECK below.
   NSInteger parent_window_number = [window_ windowNumber];
   for (BridgedNativeWidget* child: child_windows_) {
     // Note: order the child windows on top, regardless of whether or not they
     // are currently visible. They probably aren't, since the parent was hidden
     // prior to this, but they could have been made visible in other ways.
     if (child->wants_to_be_visible_) {
-      ++visible_children;
+      ++visible_bridged_children;
       // Here -[NSWindow orderWindow:relativeTo:] is used to put the window on
       // screen. However, that by itself is insufficient to guarantee a correct
       // z-order relationship. If this function is being called from a z-order
@@ -1217,7 +1232,8 @@ NSComparisonResult SubviewSorter(NSViewComparatorValue lhs,
     }
     CHECK_EQ(child_count, child_windows_.size());
   }
-  DCHECK_EQ(visible_children, [[window_ childWindows] count]);
+  DCHECK_EQ(visible_bridged_children,
+            CountBridgedWindows([window_ childWindows]));
 }
 
 gfx::Size BridgedNativeWidget::GetClientAreaSize() const {