mac: Import chromium's CustomFrameView code.

browser/ui/cocoa/custom_frame_view.h

@@ -0,0 +1,56 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import <Cocoa/Cocoa.h>
+
+// CustomFrameView is a class whose methods we swizzle into NSGrayFrame
+// on 10.7 and below, or NSThemeFrame on 10.8 and above, so that we can
+// support custom frame drawing. This is used with a textured window so that
+// AppKit does not draw a title bar.
+// This class is never to be instantiated on its own.
+// We explored a variety of ways to support custom frame drawing and custom
+// window widgets.
+// Our requirements were:
+// a) that we could fall back on standard system drawing at any time for the
+//    "default theme"
+// b) We needed to be able to draw both a background pattern, and an overlay
+//    graphic, and we need to be able to set the pattern phase of our background
+//    window.
+// c) We had to be able to support "transparent" themes, so that you could see
+//    through to the underlying windows in places without the system theme
+//    getting in the way.
+//
+// Since we want "A" we couldn't just do a transparent borderless window. At
+// least I couldn't find the right combination of HITheme calls to make it draw
+// nicely, and I don't trust that the HITheme calls are going to exist in future
+// system versions.
+// "C" precluded us from inserting a view between the system frame and the
+// the content frame in Z order. To get the transparency we actually need to
+// replace the drawing of the system frame.
+// "B" precluded us from just setting a background color on the window.
+//
+// Originally we tried overriding the private API +frameViewForStyleMask: to
+// add our own subclass of NSGrayView to our window. Turns out that if you
+// subclass NSGrayView it does not draw correctly when you call NSGrayView's
+// drawRect. It appears that NSGrayView's drawRect: method (and that of its
+// superclasses) do lots of "isMemberOfClass/isKindOfClass" calls, and if your
+// class is NOT an instance of NSGrayView (as opposed to a subclass of
+// NSGrayView) then the system drawing will not work correctly.
+//
+// Given all of the above, we found swizzling drawRect in _load to be the
+// easiest and safest method of achieving our goals. We do the best we can to
+// check that everything is safe, and attempt to fallback gracefully if it is
+// not.
+
+@interface NSWindow (CustomFrameView)
+
+// To define custom window drawing behaviour, override this method on an
+// NSWindow subclass. Call the default method (on super) to draw the
+// default frame.
+// NOTE: Always call the default implementation (even if you just immediately
+// draw over it), otherwise the top-left and top-right corners of the window
+// won't be drawn correctly.
+- (void)drawCustomFrameRect:(NSRect)rect forView:(NSView*)view;
+
+@end