Fix errors in display resolution change notifications

chrome/browser/extensions/display_info_provider_chromeos.cc

Index: chrome/browser/extensions/display_info_provider_chromeos.cc
diff --git a/chrome/browser/extensions/display_info_provider_chromeos.cc b/chrome/browser/extensions/display_info_provider_chromeos.cc
index a5a37a74f93a246a19855aaf45ad1c1d57b846b3..7e5b4c86ad9892151bd04fb9c086a4442a29058e 100644
--- a/chrome/browser/extensions/display_info_provider_chromeos.cc
+++ b/chrome/browser/extensions/display_info_provider_chromeos.cc
@@ -342,11 +342,9 @@ bool ValidateParamsForDisplay(const system_display::DisplayProperties& info,
       return false;
     }
 
-    if (!display_manager->SetDisplayMode(id, new_mode)) {
-      *error = "Unable to set the display mode.";
-      return false;
-    }
-
+    // We must prepare the notification before we set the mode, since setting
+    // the mode actually shows the notification, so it should be ready by then.
+    // crbug.com/701389.

[stevenjb, 2017/04/06 22:10:53]

This is all kind of awkward. It looks like we do this here because
DisplayManager doesn't have access to resolution_notification_controller?

Can we explain what all is going on here, e.g (I may have this wrong):
* We prepare an Ash notification here.
* If DisplayManager successfully sets the new display mode, it triggers the
actual notification (where?)
* If the user confirms the change (?) the notification calls StoreDisplayPrefs ?

[afakhry, 2017/04/07 00:04:57]

ResolutionNotificationController::OnDisplayConfigurationChanged()
Yes, in ResolutionNotificationController::AcceptResolutionChange().

This should be documented in the doc for
ResolutionNotificationController::PrepareNotification() here:
https://cs.chromium.org/chromium/src/ash/display/resolution_notification_cont...

So in order to avoid repetition of docs, please let me know what's the degree of
details you want to include here.

     if (!display::Display::IsInternalDisplayId(id)) {
       // For external displays, show a notification confirming the resolution
       // change.
@@ -355,6 +353,11 @@ bool ValidateParamsForDisplay(const system_display::DisplayProperties& info,
           ->PrepareNotification(id, current_mode, new_mode,
                                 base::Bind(&chromeos::StoreDisplayPrefs));
     }
+
+    if (!display_manager->SetDisplayMode(id, new_mode)) {
+      *error = "Unable to set the display mode.";
+      return false;
+    }
   }
   return true;
 }