Implement overscroll support for the virtual keyboard.

ui/keyboard/keyboard_util.h

Index: ui/keyboard/keyboard_util.h
diff --git a/ui/keyboard/keyboard_util.h b/ui/keyboard/keyboard_util.h
index 4e09d96e61865cc7d4af0230517c8c92a0005dbb..bc343bda7b654b5603977069bae1900296f97cc4 100644
--- a/ui/keyboard/keyboard_util.h
+++ b/ui/keyboard/keyboard_util.h
@@ -68,6 +68,9 @@ KEYBOARD_EXPORT bool IsKeyboardEnabled();
 // Returns true if the keyboard usability test is enabled.
 KEYBOARD_EXPORT bool IsKeyboardUsabilityExperimentEnabled();
 
+// Returns true if keyboard overscroll mode is enabled.
+KEYBOARD_EXPORT bool IsKeyboardOverscrollEnabled();
+
 // Returns true if an IME extension can specify a custom input view for the
 // virtual keyboard window.
 KEYBOARD_EXPORT bool IsInputViewEnabled();