add/remove displays properly on hotplug events

Bug: 7191563
Change-Id: I8f0fbf3b29658c9479443141798e6f288a1f2d52
diff --git a/services/surfaceflinger/DisplayDevice.h b/services/surfaceflinger/DisplayDevice.h
index d83625a..1d77154 100644
--- a/services/surfaceflinger/DisplayDevice.h
+++ b/services/surfaceflinger/DisplayDevice.h
@@ -119,9 +119,7 @@
     }
     inline Rect bounds() const { return getBounds(); }
 
-    void setDisplayName(const String8& displayName) {
-        mDisplayName = displayName;
-    }
+    void setDisplayName(const String8& displayName);
     const String8& getDisplayName() const { return mDisplayName; }
 
     static EGLBoolean makeCurrent(EGLDisplay dpy,