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 2df4f974938fc00b0ed8930b8fab2d0c6fdca053..072a6da4a0e19adc64ef4e0d00709102ecb5e41e 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
@@ -7,9 +7,7 @@ package org.chromium.content.browser;
 import android.content.Context;
 import android.util.TypedValue;
 
-import org.chromium.base.CommandLine;
 import org.chromium.base.VisibleForTesting;
-import org.chromium.content.common.ContentSwitches;
 
 /**
  * Cached copy of all positions and scales (CSS-to-DIP-to-physical pixels)
@@ -62,16 +60,12 @@ public class RenderCoordinates {
         mContentHeightCss = contentHeightCss;
     }
 
-    void setDeviceScaleFactor(Context context) {
-        String forceScaleFactor =
-                CommandLine.getInstance().getSwitchValue(ContentSwitches.FORCE_DEVICE_SCALE_FACTOR);
-        mDeviceScaleFactor = forceScaleFactor != null
-                ? Float.valueOf(forceScaleFactor)
-                : context.getResources().getDisplayMetrics().density;
+    void setDeviceScaleFactor(float dipScale, 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
-        // getWheelScrollScale().
+        // getWheelScrollFactor().
 
         TypedValue outValue = new TypedValue();
         // This is the same attribute used by Android Views to scale wheel