Use gfx::NativeView rather than gfx::NativeWindow to identify web contents modal dialogs

chrome/browser/ui/cocoa/constrained_window/constrained_window_mac.mm

Index: chrome/browser/ui/cocoa/constrained_window/constrained_window_mac.mm
diff --git a/chrome/browser/ui/cocoa/constrained_window/constrained_window_mac.mm b/chrome/browser/ui/cocoa/constrained_window/constrained_window_mac.mm
index 80ca7e0f4421ac7a6b8831cf8d0a20740028ec05..50d53512101aa1d0e3139cb8dac26c9027f3626a 100644
--- a/chrome/browser/ui/cocoa/constrained_window/constrained_window_mac.mm
+++ b/chrome/browser/ui/cocoa/constrained_window/constrained_window_mac.mm
@@ -24,6 +24,7 @@ ConstrainedWindowMac::ConstrainedWindowMac(
     : delegate_(delegate),
       web_contents_(web_contents),
       sheet_([sheet retain]),
+      dummyView_([NSView alloc]),
       pending_show_(false) {
   DCHECK(web_contents);
   DCHECK(sheet_.get());
@@ -76,9 +77,10 @@ void ConstrainedWindowMac::PulseWebContentsModalDialog() {
       pulseSheet:sheet_];
 }
 
-gfx::NativeWindow ConstrainedWindowMac::GetNativeWindow() {
-  NOTREACHED();
-  return nil;
+gfx::NativeView ConstrainedWindowMac::GetNativeView() {
+  // TODO(wittman): Return a NSView that is meaningful and unique to the window,
+  // and remove dummyView_.
+  return dummyView_.get();
 }
 
 void ConstrainedWindowMac::Observe(