Realign message center popups when displays are added or removed

ui/message_center/views/desktop_popup_alignment_delegate.cc

Index: ui/message_center/views/desktop_popup_alignment_delegate.cc
diff --git a/ui/message_center/views/desktop_popup_alignment_delegate.cc b/ui/message_center/views/desktop_popup_alignment_delegate.cc
index f67200def64ace65e3e331bb51c73008d401fac8..d51021d5bb75f28789ede39ed7b338c4dd7a6fcc 100644
--- a/ui/message_center/views/desktop_popup_alignment_delegate.cc
+++ b/ui/message_center/views/desktop_popup_alignment_delegate.cc
@@ -14,7 +14,7 @@ namespace message_center {
 
 DesktopPopupAlignmentDelegate::DesktopPopupAlignmentDelegate()
     : alignment_(POPUP_ALIGNMENT_BOTTOM | POPUP_ALIGNMENT_RIGHT),
-      display_id_(display::Display::kInvalidDisplayID),
+      primary_display_id_(display::Display::kInvalidDisplayID),
       screen_(NULL) {}
 
 DesktopPopupAlignmentDelegate::~DesktopPopupAlignmentDelegate() {
@@ -29,7 +29,7 @@ void DesktopPopupAlignmentDelegate::StartObserving(display::Screen* screen) {
   screen_ = screen;
   screen_->AddObserver(this);
   display::Display display = screen_->GetPrimaryDisplay();
-  display_id_ = display.id();
+  primary_display_id_ = display.id();
   RecomputeAlignment(display);
 }
 
@@ -83,19 +83,36 @@ void DesktopPopupAlignmentDelegate::RecomputeAlignment(
       : POPUP_ALIGNMENT_RIGHT;
 }
 
+// Anytime the display configuration changes, we need to recompute the alignment
+// on the primary display.
+void DesktopPopupAlignmentDelegate::UpdatePrimaryDisplay() {
+  display::Display primary_display = screen_->GetPrimaryDisplay();
+  if (primary_display.id() != primary_display_id_) {
+    primary_display_id_ = primary_display.id();
+    RecomputeAlignment(primary_display);
+    DoUpdateIfPossible();
+  }
+}
+
 void DesktopPopupAlignmentDelegate::OnDisplayAdded(
-    const display::Display& new_display) {}
+    const display::Display& added_display) {
+  // The added display could be the new primary display.
+  UpdatePrimaryDisplay();
+}
 
 void DesktopPopupAlignmentDelegate::OnDisplayRemoved(
-    const display::Display& old_display) {}
+    const display::Display& removed_display) {
+  // The removed display may have been the primary display.
+  UpdatePrimaryDisplay();
+}
 
 void DesktopPopupAlignmentDelegate::OnDisplayMetricsChanged(
     const display::Display& display,
     uint32_t metrics) {
-  if (display.id() == display_id_) {
-    RecomputeAlignment(display);
-    DoUpdateIfPossible();
-  }
+  // Set to kInvalidDisplayID so the alignment is updated regardless of whether

[dewittj, 2016/06/27 17:37:27]

Why always recompute the alignment?

[osandov, 2016/06/27 19:22:52]

I wanted to reuse the helper to handle all of the cases. We need the recompute
if the primary display changes resolution or switches to another display. If
another display resizes, we do some unnecessary work, but this seemed like the
cleanest way to implement it.

+  // the primary display actually changed.
+  primary_display_id_ = display::Display::kInvalidDisplayID;
+  UpdatePrimaryDisplay();
 }
 
 }  // namespace message_center