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 45a360b4f9da94ff9fe8607a1c29090fe6c44221..a2addf94c6e7ebeeb8ceedfd2e410c588a8384c6 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -79,6 +79,7 @@ import org.chromium.ui.base.ActivityWindowAndroid;
 import org.chromium.ui.base.PageTransition;
 import org.chromium.ui.base.ViewAndroidDelegate;
 import org.chromium.ui.base.WindowAndroid;
+import org.chromium.ui.display.DisplayAndroid.DisplayAndroidObserver;
 
 import java.io.File;
 import java.lang.annotation.Annotation;
@@ -99,8 +100,7 @@ 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 {
     private static final String TAG = "AwContents";
     private static final boolean TRACE = false;
     private static final int NO_WARN = 0;
@@ -287,6 +287,7 @@ public class AwContents implements SmartClipProvider,
     private final AwZoomControls mZoomControls;
     private final AwScrollOffsetManager mScrollOffsetManager;
     private OverScrollGlow mOverScrollGlow;
+    private final DisplayAndroidObserver mDisplayObserver;
     // This can be accessed on any thread after construction. See AwContentsIoThreadClient.
     private final AwSettings mSettings;
     private final ScrollAccessibilityHelper mScrollAccessibilityHelper;
@@ -699,6 +700,21 @@ public class AwContents implements SmartClipProvider,
     };
 
     //--------------------------------------------------------------------------------------------
+    private class AwDisplayAndroidObserver implements DisplayAndroidObserver {
+        @Override
+        public void onRotationChanged(int rotation) {}
+
+        @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);
+        }
+    };
+
+    //--------------------------------------------------------------------------------------------
     /**
      * @param browserContext the browsing context to associate this view contents with.
      * @param containerView the view-hierarchy item this object will be bound to.
@@ -770,6 +786,7 @@ public class AwContents implements SmartClipProvider,
         mBackgroundThreadClient = new BackgroundThreadClientImpl();
         mIoThreadClient = new IoThreadClientImpl();
         mInterceptNavigationDelegate = new InterceptNavigationDelegateImpl();
+        mDisplayObserver = new AwDisplayAndroidObserver();
         mUpdateVisibilityRunnable = new Runnable() {
             @Override
             public void run() {
@@ -1054,10 +1071,8 @@ public class AwContents implements SmartClipProvider,
         installWebContentsObserver();
         mSettings.setWebContents(webContents);
 
-        float dipScale = mContentViewCore.getDeviceScaleFactor();
-        nativeSetDipScale(mNativeAwContents, dipScale);
-        mLayoutSizer.setDIPScale(dipScale);
-        mSettings.setDIPScale(dipScale);
+        final float dipScale = mWindowAndroid.getWindowAndroid().getDisplay().getDIPScale();
+        mDisplayObserver.onDIPScaleChanged(dipScale);
 
         updateContentViewCoreVisibility();
 
@@ -2375,6 +2390,7 @@ public class AwContents implements SmartClipProvider,
         if (TRACE) Log.i(TAG, "%s onAttachedToWindow", this);
         mTemporarilyDetached = false;
         mAwViewMethods.onAttachedToWindow();
+        mWindowAndroid.getWindowAndroid().getDisplay().addObserver(mDisplayObserver);
     }
 
     /**
@@ -2383,6 +2399,7 @@ public class AwContents implements SmartClipProvider,
     @SuppressLint("MissingSuperCall")
     public void onDetachedFromWindow() {
         if (TRACE) Log.i(TAG, "%s onDetachedFromWindow", this);
+        mWindowAndroid.getWindowAndroid().getDisplay().removeObserver(mDisplayObserver);
         mAwViewMethods.onDetachedFromWindow();
     }