Implement overscroll support for the virtual keyboard.

ui/keyboard/keyboard_util.cc

Index: ui/keyboard/keyboard_util.cc
diff --git a/ui/keyboard/keyboard_util.cc b/ui/keyboard/keyboard_util.cc
index 4d717395518935a833792b0ab5ff0a23f55bda5a..60431b03c48748b6bd80956df6cf8e4a62b713e6 100644
--- a/ui/keyboard/keyboard_util.cc
+++ b/ui/keyboard/keyboard_util.cc
@@ -103,6 +103,22 @@ bool IsKeyboardUsabilityExperimentEnabled() {
       switches::kKeyboardUsabilityExperiment);
 }
 
+bool IsKeyboardOverscrollEnabled() {
+  if (!IsKeyboardEnabled())
+    return false;
+  if (g_accessibility_keyboard_enabled)
+    return false;
+  if (CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kDisableVirtualKeyboardOverscroll)) {
+    return false;
+  }
+  if (CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableVirtualKeyboardOverscroll)) {
+    return true;
+  }
+  return false;
+}
+
 bool InsertText(const base::string16& text, aura::Window* root_window) {
   if (!root_window)
     return false;