For OSX, make it so that notifications only start resizing after the first paint is done.

chrome/browser/notifications/balloon.cc

 // Copyright (c) 2009 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.
 
 #include "chrome/browser/notifications/balloon.h"
 
 #include "base/logging.h"
 #include "chrome/browser/notifications/balloon_collection.h"
 #include "chrome/browser/notifications/notification.h"
 #include "chrome/browser/renderer_host/site_instance.h"
 #include "gfx/rect.h"
+#include "gfx/size.h"
 
 Balloon::Balloon(const Notification& notification, Profile* profile,
                  BalloonCollection* collection)
     : profile_(profile),
       notification_(new Notification(notification)),
       collection_(collection) {
 }
 
 Balloon::~Balloon() {
 }
 
 void Balloon::SetPosition(const gfx::Point& upper_left, bool reposition) {
   position_ = upper_left;
   if (reposition && balloon_view_.get())
     balloon_view_->RepositionToBalloon();
 }
 
 void Balloon::SetContentPreferredSize(const gfx::Size& size) {
-  collection_->ResizeBalloon(this, size);
+  gfx::Size new_size(size);
+#if defined(OS_MACOSX)

[John Gregg, 2010/11/30 00:25:22]

add comment with a TODO and bug # about making this cross-platform

+  // Only allow the size of notifications to grow.  This stops the balloon
+  // from jumping between sizes due to dynamic content.  For example, the
+  // balloon's contents may adjust due to changes in
+  // document.body.clientHeight.
+  new_size.set_height(std::max(new_size.height(), content_size_.height()));
+
+  if (content_size_ == new_size)
+    return;
+#endif
+  collection_->ResizeBalloon(this, new_size);
 }
 
 void Balloon::set_view(BalloonView* balloon_view) {
   balloon_view_.reset(balloon_view);
 }
 
 void Balloon::Show() {
   notification_->Display();
   if (balloon_view_.get()) {
     balloon_view_->Show(this);
@@ skipping 18 matching lines @@
   notification_->Close(by_user);
   collection_->OnBalloonClosed(this);
 }
 
 void Balloon::CloseByScript() {
   // A user-initiated close begins with the view and then closes this object;
   // we simulate that with a script-initiated close but pass |by_user|=false.
   DCHECK(balloon_view_.get());
   balloon_view_->Close(false);
 }