Fix DropdownPopupWindow's position in Android N.

ui/android/java/src/org/chromium/ui/DropdownPopupWindow.java

Index: ui/android/java/src/org/chromium/ui/DropdownPopupWindow.java
diff --git a/ui/android/java/src/org/chromium/ui/DropdownPopupWindow.java b/ui/android/java/src/org/chromium/ui/DropdownPopupWindow.java
index 4258a0c806a76e287ab84784002ce88aba744dda..45b799e33ece7d4e5a067421924f246b75afcbf4 100644
--- a/ui/android/java/src/org/chromium/ui/DropdownPopupWindow.java
+++ b/ui/android/java/src/org/chromium/ui/DropdownPopupWindow.java
@@ -35,6 +35,7 @@ public class DropdownPopupWindow extends ListPopupWindow {
     private float mAnchorX;
     private float mAnchorY;
     private boolean mRtl;
+    private int mInitialSelection = -1;
     private OnLayoutChangeListener mLayoutChangeListener;
     private PopupWindow.OnDismissListener mOnDismissListener;
     private CharSequence mDescription;
@@ -107,6 +108,11 @@ public class DropdownPopupWindow extends ListPopupWindow {
         super.setAdapter(adapter);
     }
 
+
+    public void setInitialSelection(int initialSelection) {
+        mInitialSelection = initialSelection;
+    }
+
     /**
      * Shows the popup. The adapter should be set before calling this method.
      */
@@ -141,6 +147,10 @@ public class DropdownPopupWindow extends ListPopupWindow {
             getListView().setContentDescription(mDescription);
             getListView().sendAccessibilityEvent(AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED);
         }
+        if (mInitialSelection >= 0) {
+            getListView().setSelection(mInitialSelection);
+            mInitialSelection = -1;
+        }
     }
 
     @Override