MacViews: Exploring removal of window-modal sheets.

chrome/browser/ui/cocoa/web_contents_modal_dialog_host_cocoa.mm

Index: chrome/browser/ui/cocoa/web_contents_modal_dialog_host_cocoa.mm
diff --git a/chrome/browser/ui/cocoa/web_contents_modal_dialog_host_cocoa.mm b/chrome/browser/ui/cocoa/web_contents_modal_dialog_host_cocoa.mm
index 82fab3d83c7e3bb1bedded403307e9e14c2bdcc3..b77e262d5e82c4d35c6e03d41a17fed8cc118c22 100644
--- a/chrome/browser/ui/cocoa/web_contents_modal_dialog_host_cocoa.mm
+++ b/chrome/browser/ui/cocoa/web_contents_modal_dialog_host_cocoa.mm
@@ -10,6 +10,7 @@
 #import "chrome/browser/ui/cocoa/constrained_window/constrained_window_sheet_controller.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/size.h"
+#import "ui/gfx/mac/coordinate_conversion.h"
 
 WebContentsModalDialogHostCocoa::WebContentsModalDialogHostCocoa(
     ConstrainedWindowSheetController* sheet_controller)
@@ -17,8 +18,13 @@ WebContentsModalDialogHostCocoa::WebContentsModalDialogHostCocoa(
 }
 
 WebContentsModalDialogHostCocoa::~WebContentsModalDialogHostCocoa() {
-  // Toolkit-Views calls OnHostDestroying on observers here, but the Cocoa host
-  // doesn't need to be observed.
+  for (auto& observer : observers_)
+    observer.OnHostDestroying();
+}
+
+void WebContentsModalDialogHostCocoa::OnPositionRequiresUpdate() {
+  for (auto& observer : observers_)
+    observer.OnPositionRequiresUpdate();
 }
 
 gfx::NativeView WebContentsModalDialogHostCocoa::GetHostView() const {
@@ -42,18 +48,39 @@ gfx::NativeView WebContentsModalDialogHostCocoa::GetHostView() const {
 
 gfx::Point WebContentsModalDialogHostCocoa::GetDialogPosition(
     const gfx::Size& size) {
-  // Dialogs are always re-positioned by the constrained window sheet controller
-  // so nothing interesting to return yet.
-  return gfx::Point();
+  // Web-modals go via [sheet_controller_ originForSheet:..]. This is invoked
+  // for window-modals, so use the NSWindow sheet APIs.
+  NSWindow* native_parent = [sheet_controller_ parentWindow];
+  NSRect proposed_rect = [[native_parent contentView] bounds];
+  proposed_rect.origin.y = proposed_rect.size.height;
+  proposed_rect.size.height = 0;
+
+  id parent_delegate = [native_parent delegate];
+  if ([parent_delegate
+          respondsToSelector:@selector(window:willPositionSheet:usingRect:)]) {
+    proposed_rect = [parent_delegate window:native_parent
+                          willPositionSheet:nil
+                                  usingRect:proposed_rect];
+  }
+
+  // Center horizontally and flip vertically. Note that origin.x may go
+  // negative. (That means it can also go offscreen.)
+  return gfx::Point(NSMidX(proposed_rect) - size.width() / 2,
+                    NSHeight([native_parent frame]) - proposed_rect.origin.y);
+}
+
+gfx::Point WebContentsModalDialogHostCocoa::GetHostPosition() const {
+  return gfx::ScreenRectFromNSRect([[sheet_controller_ parentWindow] frame])
+      .origin();
 }
 
 void WebContentsModalDialogHostCocoa::AddObserver(
     web_modal::ModalDialogHostObserver* observer) {
-  NOTREACHED();
+  observers_.AddObserver(observer);
 }
 void WebContentsModalDialogHostCocoa::RemoveObserver(
     web_modal::ModalDialogHostObserver* observer) {
-  NOTREACHED();
+  observers_.RemoveObserver(observer);
 }
 
 gfx::Size WebContentsModalDialogHostCocoa::GetMaximumDialogSize() {