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 387d4a5cc26697eaa23a9dd7e73aefed84a2bda7..ad1d11e0160369e0ae6a3d87319a64c27193edd9 100644
--- a/content/browser/android/content_view_core_impl.h
+++ b/content/browser/android/content_view_core_impl.h
@@ -224,6 +224,11 @@ class ContentViewCoreImpl : public ContentViewCore,
                 const base::android::JavaParamRef<jobject>& obj,
                 jboolean focused);
 
+  void SetDIPScale(JNIEnv* env,
+                   const base::android::JavaParamRef<jobject>& obj,
+                   jfloat dipScale,
+                   jboolean forceLayout);
+
   jint GetBackgroundColor(JNIEnv* env, jobject obj);
   void SetAllowJavascriptInterfacesInspection(
       JNIEnv* env,
@@ -415,6 +420,7 @@ class ContentViewCoreImpl : public ContentViewCore,
   // --------------------------------------------------------------------------
 
   void InitWebContents();
+  void ForceLayout();
 
   RenderWidgetHostViewAndroid* GetRenderWidgetHostViewAndroid() const;
 
@@ -453,7 +459,7 @@ 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_;