Add observers for DIP scale change.

android_webview/java/src/org/chromium/android_webview/AwContents.java

Index: android_webview/java/src/org/chromium/android_webview/AwContents.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwContents.java b/android_webview/java/src/org/chromium/android_webview/AwContents.java
index 64f957629819ae073a7fa5a0b1ce869a19640fdb..0f93669bf461375e04fb0c7860db45d9d499ea3b 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -72,6 +72,7 @@ import org.chromium.content_public.common.Referrer;
 import org.chromium.net.NetError;
 import org.chromium.net.NetworkChangeNotifier;
 import org.chromium.ui.base.ActivityWindowAndroid;
+import org.chromium.ui.base.DIPScaleListener;
 import org.chromium.ui.base.PageTransition;
 import org.chromium.ui.base.ViewAndroidDelegate;
 import org.chromium.ui.base.WindowAndroid;
@@ -96,8 +97,8 @@ import java.util.concurrent.Callable;
  * continuous build & test in the open source SDK-based tree).
  */
 @JNINamespace("android_webview")
-public class AwContents implements SmartClipProvider,
-        PostMessageSender.PostMessageSenderDelegate {
+public class AwContents implements SmartClipProvider, PostMessageSender.PostMessageSenderDelegate,
+                                   DIPScaleListener {
     private static final String TAG = "AwContents";
     private static final boolean TRACE = false;
     private static final int NO_WARN = 0;
@@ -1061,12 +1062,7 @@ public class AwContents implements SmartClipProvider,
         installWebContentsObserver();
         mSettings.setWebContents(webContents);
 
-        float dipScale = mContentViewCore.getDeviceScaleFactor();
-        nativeSetDipScale(mNativeAwContents, dipScale);
-        mLayoutSizer.setDIPScale(dipScale);
-        mSettings.setDIPScale(dipScale);
-
-        updateContentViewCoreVisibility();
+        onDIPScaleChanged(mWindowAndroid.getWindowAndroid().getDIPScale());
 
         // The native side object has been bound to this java instance, so now is the time to
         // bind all the native->java relationships.
@@ -2284,6 +2280,16 @@ public class AwContents implements SmartClipProvider,
                 sentPortIds);
     }
 
+    // Implements DIPScaleListener interface method.
+    @Override
+    public void onDIPScaleChanged(float dipScale) {
+        if (TRACE) Log.i(TAG, "%s onDIPScaleChanged dipScale=%f", this, dipScale);
+
+        nativeSetDipScale(mNativeAwContents, dipScale);
+        mLayoutSizer.setDIPScale(dipScale);
+        mSettings.setDIPScale(dipScale);
+    }
+
     /**
      * Creates a message channel and returns the ports for each end of the channel.
      */
@@ -2393,6 +2399,7 @@ public class AwContents implements SmartClipProvider,
         if (TRACE) Log.i(TAG, "%s onAttachedToWindow", this);
         mTemporarilyDetached = false;
         mAwViewMethods.onAttachedToWindow();
+        mWindowAndroid.getWindowAndroid().addDIPScaleListener(this);
     }
 
     /**
@@ -2401,6 +2408,7 @@ public class AwContents implements SmartClipProvider,
     @SuppressLint("MissingSuperCall")
     public void onDetachedFromWindow() {
         if (TRACE) Log.i(TAG, "%s onDetachedFromWindow", this);
+        mWindowAndroid.getWindowAndroid().removeDIPScaleListener(this);
         mAwViewMethods.onDetachedFromWindow();
     }