[MacViews] Implement AlwaysOnTop and VisibleOnAllWorkspaces.

ui/gfx/mac/nswindow_frame_controls.mm

Index: ui/gfx/mac/nswindow_frame_controls.mm
diff --git a/ui/gfx/mac/nswindow_frame_controls.mm b/ui/gfx/mac/nswindow_frame_controls.mm
index 34f7d266516c823bc53ea6f612eee9dc22446057..e1983daa2d25a9c0b7d6def9bcdf6a00b7d32cc3 100644
--- a/ui/gfx/mac/nswindow_frame_controls.mm
+++ b/ui/gfx/mac/nswindow_frame_controls.mm
@@ -22,6 +22,13 @@ void SetResizableStyleMask(NSWindow* window, bool resizable) {
   [window setStyleMask:style_mask];
 }
 
+// Returns the level for windows that are configured to be always on top.
+// This is not a constant because NSFloatingWindowLevel is a macro defined
+// as a function call.
+NSInteger AlwaysOnTopWindowLevel() {
+  return NSFloatingWindowLevel;
+}
+
 }  // namespace
 
 namespace gfx {
@@ -35,6 +42,32 @@ void SetNSWindowCanFullscreen(NSWindow* window, bool allow_fullscreen) {
   [window setCollectionBehavior:behavior];
 }
 
+bool IsNSWindowAlwaysOnTop(NSWindow* window) {
+  return [window level] == AlwaysOnTopWindowLevel();
+}
+
+void SetNSWindowAlwaysOnTop(NSWindow* window,
+                            bool always_on_top) {
+  [window setLevel:(always_on_top ? AlwaysOnTopWindowLevel()
+                                  : NSNormalWindowLevel)];
+  // Since always-on-top windows have a higher window level than
+  // NSNormalWindowLevel, they will default to
+  // NSWindowCollectionBehaviorTransient. Set the value explicitly here to match
+  // normal windows.
+  NSWindowCollectionBehavior behavior =
+      [window collectionBehavior] | NSWindowCollectionBehaviorManaged;
+  [window setCollectionBehavior:behavior];
+}
+
+void SetNSWindowVisibleOnAllWorkspaces(NSWindow* window, bool always_visible) {
+  NSWindowCollectionBehavior behavior = [window collectionBehavior];
+  if (always_visible)
+    behavior |= NSWindowCollectionBehaviorCanJoinAllSpaces;
+  else
+    behavior &= ~NSWindowCollectionBehaviorCanJoinAllSpaces;
+  [window setCollectionBehavior:behavior];
+}
+
 void ApplyNSWindowSizeConstraints(NSWindow* window,
                                   const gfx::Size& min_size,
                                   const gfx::Size& max_size,