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..ef33c64f08a1d017a9e3fcb47bdf1cafabf2b7cd 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 +8,6 @@ import android.content.Context;
 import android.util.TypedValue;
 
 import org.chromium.base.VisibleForTesting;
-import org.chromium.ui.base.WindowAndroid;
 
 /**
  * Cached copy of all positions and scales (CSS-to-DIP-to-physical pixels)
@@ -61,14 +60,13 @@ public class RenderCoordinates {
         mContentHeightCss = contentHeightCss;
     }
 
-    void updateDeviceScaleFactorFromWindow(WindowAndroid windowAndroid) {
-        mDeviceScaleFactor = windowAndroid.getDisplay().getDIPScale();
+    void setDeviceScaleFactor(float dipScale, Context context) {

[boliu, 2016/10/18 00:26:25]

maybe should pass in WeakReference<Context> to make it clear it might be null..?

[Tima Vaisburd, 2016/10/19 01:15:54]

Done.

+        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.