Fix scroll restoration when exiting fullscreen mode.

chrome/browser/ui/exclusive_access/fullscreen_controller.cc

Index: chrome/browser/ui/exclusive_access/fullscreen_controller.cc
diff --git a/chrome/browser/ui/exclusive_access/fullscreen_controller.cc b/chrome/browser/ui/exclusive_access/fullscreen_controller.cc
index 3c7018ccf49f8d54c38ee112054071ec6037fc46..ed68d08bd5e78207cb9868c690367f266dfa15c1 100644
--- a/chrome/browser/ui/exclusive_access/fullscreen_controller.cc
+++ b/chrome/browser/ui/exclusive_access/fullscreen_controller.cc
@@ -25,6 +25,7 @@
 #include "content/public/browser/navigation_entry.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/render_view_host.h"
+#include "content/public/browser/render_widget_host.h"
 #include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/user_metrics.h"
 #include "content/public/browser/web_contents.h"
@@ -37,6 +38,8 @@
 
 using base::UserMetricsAction;
 using content::RenderViewHost;
+using content::RenderWidgetHost;
+using content::RenderWidgetHostView;
 using content::WebContents;
 
 FullscreenController::FullscreenController(ExclusiveAccessManager* manager)
@@ -218,6 +221,17 @@ void FullscreenController::ExitFullscreenModeForTab(WebContents* web_contents) {
   // This is only a change between Browser and Tab fullscreen. We generate
   // a fullscreen notification now because there is no window change.
   PostFullscreenChangeNotification(true);
+
+  // Ensure web contents exit fullscreen state by sending a resize message,

[scheib, 2015/12/01 00:30:18]

I'm a bit wondering why this isn't part of ::NotifyTabExclusiveAccessLost and
then ExitFullscreen calling ExitFullscreenMode. I haven't traced through yet to
see why the call is needed to be moved here instead of web_contents. Calling
from FullscreenController feels as if the implementation details of WebContents
are too exposed. 

[bokan, 2015/12/01 20:46:10]

I rarely dwell in these parts so it's entirely likely this code doesn't belong
here. The reason it was a problem before is that WasResized gets called even if
we're going from Tab Fullscreen -> Normal but that would happen before the
renderer bounds would change. So the renderer would get a resize IPC with
"is_fullscreen" toggled. Then it would get a second resize with the bounds
changed. This is a problem because the renderer then doesn't know when to
restore the pre-fullscreen state without resorting to some awkward bookkeeping .

I've uploaded a new patch that instead passes a parameter through to
WebContents::ExitFullscreen that tells it whether exiting fullscreen will cause
the bounds to change. That way WebContents can then decide whether or not to
send the WasResized. I'm happy to move it elsewhere if it makes more sense, any
suggestions?

+  // which includes the fullscreen state. This is required for the situation
+  // of the browser moving the view into a fullscreen state "browser fullscreen"
+  // and then the contents entering "tab fullscreen". Exiting the contents
+  // "tab fullscreen" then won't have the side effect of the view resizing,
+  // hence the explicit call here is required.
+  if (RenderWidgetHostView* rwhv = web_contents->GetRenderWidgetHostView()) {
+      if (RenderWidgetHost* render_widget_host = rwhv->GetRenderWidgetHost())
+        render_widget_host->WasResized();
+  }
 }
 
 #if defined(OS_WIN)