[Payments] Fix credit card scanning billing address bug.

chrome/android/java/src/org/chromium/chrome/browser/payments/ui/EditorDropdownField.java

Index: chrome/android/java/src/org/chromium/chrome/browser/payments/ui/EditorDropdownField.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/payments/ui/EditorDropdownField.java b/chrome/android/java/src/org/chromium/chrome/browser/payments/ui/EditorDropdownField.java
index 6113e9b980407f10c4da686b17d2e28e2a0ae1b0..e99cb942c825f63b07ebf7558d382fe6f78b5c90 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/payments/ui/EditorDropdownField.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/payments/ui/EditorDropdownField.java
@@ -144,8 +144,15 @@ class EditorDropdownField implements EditorFieldView {
 
     @Override
     public void update() {
-        mSelectedIndex =
+        // If the adapter supports a hint and no value was selected, select the hint.
+        if (mFieldModel.getHint() != null && mFieldModel.getValue() == null) {
+            // The hint is hidden right after the last element.
+            mSelectedIndex = mFieldModel.getDropdownKeyValues().size();
+        } else {
+            mSelectedIndex =
                 getDropdownIndex(mFieldModel.getDropdownKeyValues(), mFieldModel.getValue());
+        }
+
         mDropdown.setSelection(mSelectedIndex);
     }