Add observers for DIP scale change.

content/public/android/java/src/org/chromium/content/browser/RenderCoordinates.java

Index: content/public/android/java/src/org/chromium/content/browser/RenderCoordinates.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/RenderCoordinates.java b/content/public/android/java/src/org/chromium/content/browser/RenderCoordinates.java
index 5bcebc28c86b732dac67dbb830cd7e9c03ab5c00..cbdadf9fdb90ccb1746232779b4d460a7adc8f3c 100644
--- a/content/public/android/java/src/org/chromium/content/browser/RenderCoordinates.java
+++ b/content/public/android/java/src/org/chromium/content/browser/RenderCoordinates.java
@@ -8,7 +8,8 @@ import android.content.Context;
 import android.util.TypedValue;
 
 import org.chromium.base.VisibleForTesting;
-import org.chromium.ui.base.WindowAndroid;
+
+import java.lang.ref.WeakReference;
 
 /**
  * Cached copy of all positions and scales (CSS-to-DIP-to-physical pixels)
@@ -38,7 +39,7 @@ public class RenderCoordinates {
     private float mMaxPageScaleFactor = 1.0f;
 
     // Cached device density.
-    private float mDeviceScaleFactor;
+    private float mDeviceScaleFactor = 1.0f;
 
     // Multiplier that determines how many (device) pixels to scroll per mouse
     // wheel tick. Defaults to the preferred list item height.
@@ -61,20 +62,20 @@ public class RenderCoordinates {
         mContentHeightCss = contentHeightCss;
     }
 
-    void updateDeviceScaleFactorFromWindow(WindowAndroid windowAndroid) {
-        mDeviceScaleFactor = windowAndroid.getDisplay().getDIPScale();
+    void setDeviceScaleFactor(float dipScale, WeakReference<Context> context) {
+        mDeviceScaleFactor = dipScale;
 
         // The wheel scroll factor depends on the theme in the context.
         // This code assumes that the theme won't change between this call and
         // getWheelScrollFactor().
 
-        Context context = windowAndroid.getContext().get();
         TypedValue outValue = new TypedValue();
         // This is the same attribute used by Android Views to scale wheel
         // event motion into scroll deltas.
-        if (context != null && context.getTheme().resolveAttribute(
+        if (context.get() != null && context.get().getTheme().resolveAttribute(

[boliu, 2016/10/19 04:19:19]

you need to call get() first and save it in a local var first, because in
theory, it's possible the context gets collected between this check and the next
clause when it's used

[Tima Vaisburd, 2016/10/19 20:25:11]

Thank you! Done.

                 android.R.attr.listPreferredItemHeight, outValue, true)) {
-            mWheelScrollFactor = outValue.getDimension(context.getResources().getDisplayMetrics());
+            mWheelScrollFactor = outValue.getDimension(
+                    context.get().getResources().getDisplayMetrics());
         } else {
             // If attribute retrieval fails, just use a sensible default.
             mWheelScrollFactor = 64 * mDeviceScaleFactor;