Implement overscroll support for the virtual keyboard.

ui/keyboard/keyboard_util.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/keyboard/keyboard_util.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
@@ skipping 85 matching lines @@
       CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kEnableVirtualKeyboard) ||
       IsKeyboardUsabilityExperimentEnabled();
 }
 
 bool IsKeyboardUsabilityExperimentEnabled() {
   return CommandLine::ForCurrentProcess()->HasSwitch(
       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;
 
   ui::InputMethod* input_method = root_window->GetProperty(
       aura::client::kRootWindowInputMethodKey);
   if (!input_method)
     return false;
 
   ui::TextInputClient* tic = input_method->GetTextInputClient();
@@ skipping 198 matching lines @@
 }
 
 void LogKeyboardControlEvent(KeyboardControlEvent event) {
   UMA_HISTOGRAM_ENUMERATION(
       "VirtualKeyboard.KeyboardControlEvent",
       event,
       keyboard::KEYBOARD_CONTROL_MAX);
 }
 
 }  // namespace keyboard