Add observers for DIP scale change.

content/browser/android/content_view_core_impl.h

Index: content/browser/android/content_view_core_impl.h
diff --git a/content/browser/android/content_view_core_impl.h b/content/browser/android/content_view_core_impl.h
index d425cc015d21ab566e6643b2e24349858d3d5ea1..cd1c84de186b9dbfde356bdd6dc78ff5300318c6 100644
--- a/content/browser/android/content_view_core_impl.h
+++ b/content/browser/android/content_view_core_impl.h
@@ -229,6 +229,10 @@ class ContentViewCoreImpl : public ContentViewCore,
                 const base::android::JavaParamRef<jobject>& obj,
                 jboolean focused);
 
+  void SetDIPScale(JNIEnv* env,
+                   const base::android::JavaParamRef<jobject>& obj,
+                   jfloat dipScale);
+
   jint GetBackgroundColor(JNIEnv* env, jobject obj);
   void SetAllowJavascriptInterfacesInspection(
       JNIEnv* env,
@@ -460,7 +464,7 @@ class ContentViewCoreImpl : public ContentViewCore,
   float page_scale_;
 
   // Device scale factor.
-  const float dpi_scale_;
+  float dpi_scale_;
 
   // Observer to notify of lifecyle changes.
   base::ObserverList<ContentViewCoreImplObserver> observer_list_;