Fix use after free for cached_displays_.

ui/display/manager/chromeos/test/test_native_display_delegate.cc

Index: ui/display/manager/chromeos/test/test_native_display_delegate.cc
diff --git a/ui/display/manager/chromeos/test/test_native_display_delegate.cc b/ui/display/manager/chromeos/test/test_native_display_delegate.cc
index 060dec2dfbfa599e82a082575e51ac14f295b957..9cd1bda4897fafa58aa03009d95a64112241aec9 100644
--- a/ui/display/manager/chromeos/test/test_native_display_delegate.cc
+++ b/ui/display/manager/chromeos/test/test_native_display_delegate.cc
@@ -10,6 +10,7 @@
 #include "base/threading/thread_task_runner_handle.h"
 #include "ui/display/manager/chromeos/test/action_logger.h"
 #include "ui/display/types/display_mode.h"
+#include "ui/display/types/native_display_observer.h"
 
 namespace ui {
 namespace test {
@@ -62,6 +63,10 @@ void TestNativeDisplayDelegate::ForceDPMSOn() {
 
 void TestNativeDisplayDelegate::GetDisplays(
     const GetDisplaysCallback& callback) {
+  // This mimics the behavior of Ozone DRM when new display state arrives.
+  for (NativeDisplayObserver& observer : observers_)
+    observer.OnDisplaySnapshotsInvalidated();
+
   if (run_async_) {
     base::ThreadTaskRunnerHandle::Get()->PostTask(
         FROM_HERE, base::Bind(callback, outputs_));
@@ -144,10 +149,14 @@ bool TestNativeDisplayDelegate::SetColorCorrection(
   return true;
 }
 
-void TestNativeDisplayDelegate::AddObserver(NativeDisplayObserver* observer) {}
+void TestNativeDisplayDelegate::AddObserver(NativeDisplayObserver* observer) {
+  observers_.AddObserver(observer);
+}
 
 void TestNativeDisplayDelegate::RemoveObserver(
-    NativeDisplayObserver* observer) {}
+    NativeDisplayObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
 
 display::FakeDisplayController*
 TestNativeDisplayDelegate::GetFakeDisplayController() {