JavaScript dialogs cause a page to lose fullscreen.

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index ffba46b099c9192c32330841cccdb96e87b58595..3aab619ff9329469d8e8961bbc9e56591128cb9f 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -4425,6 +4425,11 @@ void WebContentsImpl::RunJavaScriptDialog(RenderFrameHost* render_frame_host,
                                           const GURL& frame_url,
                                           JavaScriptDialogType dialog_type,
                                           IPC::Message* reply_msg) {
+  // Running a dialog causes an exit to webpage-initiated fullscreen.
+  // http://crbug.com/728276
+  if (IsFullscreenForCurrentTab())
+    ExitFullscreen(true);
+
   // Suppress JavaScript dialogs when requested. Also suppress messages when
   // showing an interstitial as it's shown over the previous page and we don't
   // want the hidden page's dialogs to interfere with the interstitial.
@@ -4457,6 +4462,11 @@ void WebContentsImpl::RunBeforeUnloadConfirm(
     RenderFrameHost* render_frame_host,
     bool is_reload,
     IPC::Message* reply_msg) {
+  // Running a dialog causes an exit to webpage-initiated fullscreen.
+  // http://crbug.com/728276
+  if (IsFullscreenForCurrentTab())
+    ExitFullscreen(true);
+
   RenderFrameHostImpl* rfhi =
       static_cast<RenderFrameHostImpl*>(render_frame_host);
   if (delegate_)