Alternative: access the WebContentsView directly without an interface method.

chrome/browser/ui/cocoa/extensions/shell_window_cocoa.mm

Index: chrome/browser/ui/cocoa/extensions/shell_window_cocoa.mm
diff --git a/chrome/browser/ui/cocoa/extensions/shell_window_cocoa.mm b/chrome/browser/ui/cocoa/extensions/shell_window_cocoa.mm
index 479114c31a81bbb470f150af05ffa3fdd2f05708..e32d6a84901f728930009afb017d97d09aa291a4 100644
--- a/chrome/browser/ui/cocoa/extensions/shell_window_cocoa.mm
+++ b/chrome/browser/ui/cocoa/extensions/shell_window_cocoa.mm
@@ -72,6 +72,21 @@
 
 @end
 
+@interface ControlRegionView : NSView
+@end
+@implementation ControlRegionView
+- (BOOL)mouseDownCanMoveWindow {
+  return NO;
+}
+- (NSView*)hitTest:(NSPoint)aPoint {
+  return nil;
+}
+@end
+
+@interface NSView (WebContentsView)
+- (void)setMouseDownCanMoveWindow:(BOOL)can_move;
+@end
+
 ShellWindowCocoa::ShellWindowCocoa(Profile* profile,
                                    const extensions::Extension* extension,
                                    const GURL& url,
@@ -108,9 +123,33 @@ ShellWindowCocoa::ShellWindowCocoa(Profile* profile,
     [window setBottomCornerRounded:NO];
 
   NSView* view = web_contents()->GetView()->GetNativeView();
-  [view setFrame:[[window contentView] bounds]];
   [view setAutoresizingMask:NSViewWidthSizable | NSViewHeightSizable];
-  [[window contentView] addSubview:view];
+  if (params.frame == ShellWindow::CreateParams::FRAME_CHROME) {
+    [view setFrame:[[window contentView] bounds]];
+    [[window contentView] addSubview:view];
+  } else {
+    NSView* web_contents_view =
+        web_contents()->GetView()->GetNativeView();
+    DCHECK([web_contents_view
+        respondsToSelector:@selector(setMouseDownCanMoveWindow:)]);
+    [web_contents_view setMouseDownCanMoveWindow:YES];
+    NSView* frameView = [[window contentView] superview];
+    [view setFrame:[frameView bounds]];
+    [frameView addSubview:view];
+    [[window standardWindowButton:NSWindowZoomButton] setHidden:YES];
+    [[window standardWindowButton:NSWindowMiniaturizeButton] setHidden:YES];
+    [[window standardWindowButton:NSWindowCloseButton] setHidden:YES];
+
+    // TODO(jeremya): this is a temporary hack to allow moving the window while
+    // we still don't have proper draggable region support.
+    NSView* controlRegion = [[ControlRegionView alloc] init];
+    [controlRegion setFrame:NSMakeRect(0, 0, NSWidth([frameView bounds]),
+                                       NSHeight([frameView bounds]) - 20)];
+    [controlRegion setAutoresizingMask:
+        NSViewWidthSizable | NSViewHeightSizable];
+    [frameView addSubview:controlRegion];
+    [controlRegion release];
+  }
 
   window_controller_.reset(
       [[ShellWindowController alloc] initWithWindow:window.release()]);