Add observers for DIP scale change.

components/external_video_surface/BUILD.gn

Index: components/external_video_surface/BUILD.gn
diff --git a/components/external_video_surface/BUILD.gn b/components/external_video_surface/BUILD.gn
index f8d45345005385d8f67af7f6b63760d5fefd3874..e99cbfeac93f21b7490b5ec054303397fbb730bc 100644
--- a/components/external_video_surface/BUILD.gn
+++ b/components/external_video_surface/BUILD.gn
@@ -30,6 +30,7 @@ if (is_android) {
     deps = [
       "//base:base_java",
       "//content/public/android:content_java",
+      "//ui/android:ui_java",

[boliu, 2016/09/14 04:35:32]

what does this have to do with this CL?

[Tima Vaisburd, 2016/09/15 00:05:03]

I do not know myself. I have a build problem that this dependency does not
propagate. It cannot see DisplayObserver.

Which makes me think: maybe ContentViewCore should not inherit DisplayObserver,
and instead contain it?

[boliu, 2016/09/15 05:27:41]

That's not ok. Understand the issue, not patch a random fix in that just makes
the problem worse.
Shouldn't matter either way I think

[Tima Vaisburd, 2016/09/16 23:59:25]

Acknowledged.

     ]
   }
   generate_jni("jni_headers") {