add/remove displays properly on hotplug events

Bug: 7191563
Change-Id: I8f0fbf3b29658c9479443141798e6f288a1f2d52
diff --git a/services/surfaceflinger/DisplayDevice.cpp b/services/surfaceflinger/DisplayDevice.cpp
index 330e09d..81ce27e 100644
--- a/services/surfaceflinger/DisplayDevice.cpp
+++ b/services/surfaceflinger/DisplayDevice.cpp
@@ -167,6 +167,13 @@
     setProjection(DisplayState::eOrientationDefault, mViewport, mFrame);
 }
 
+void DisplayDevice::setDisplayName(const String8& displayName) {
+    if (!displayName.isEmpty()) {
+        // never override the name with an empty name
+        mDisplayName = displayName;
+    }
+}
+
 uint32_t DisplayDevice::getPageFlipCount() const {
     return mPageFlipCount;
 }