Add observers for DIP scale change.

content/public/test/android/BUILD.gn

Index: content/public/test/android/BUILD.gn
diff --git a/content/public/test/android/BUILD.gn b/content/public/test/android/BUILD.gn
index 8039fc324d6254a63a295ad68bfce6f724f21b84..a9cde63340d41a620cb14495f838548f02b4bf2f 100644
--- a/content/public/test/android/BUILD.gn
+++ b/content/public/test/android/BUILD.gn
@@ -26,6 +26,7 @@ android_library("content_java_test_support") {
     "//base:base_java_test_support",
     "//content/public/android:content_java",
     "//device/geolocation:geolocation_java_test_support",
+    "//ui/android:ui_java",

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

hmm, why is this needed suddenly?

[Tima Vaisburd, 2016/09/15 00:05:04]

Same unsolved dependency.
Actually, here is a chance to ask a question: 
//content/public/android:content_java already depends on //base:base_java, but
the latter is included here as well. Maybe dependencies do not propagate?

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

That's right, dependencies do *not* propagate. The rule is you explicitly depend
on what you directly use. So if this code uses any base stuff directly, then
base should be included here. But if this code only uses base transitively
through some dependency, then having a transitive dependency should be fine.

I don't see any test changes though, so why is this needed?

[Tima Vaisburd, 2016/09/15 18:11:42]

My *guess* is that now |ContentViewCore implement ui::DisplayObserver|, and so
whenever system sees CVC it also thinks ui::DisplayObserver is used directly.
Before this change CVC subclassed content stuff mostly (i.e. not ui).
If this is true, I see two ways: add dependency in many BUILD.gn files, or make
ui::DisplayObserver an implementation detail of CVC.

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

I moved DisplayObserver from public interface the CVC inherits from into CVC
member (i.e. containment) and it fixed the compilation issue.

   ]
   java_files = [
     "javatests/src/org/chromium/content/browser/test/NativeLibraryTestBase.java",