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 96 matching lines @@
           switches::kEnableVirtualKeyboard) ||
       IsKeyboardUsabilityExperimentEnabled() ||
       g_touch_keyboard_enabled;
 }
 
 bool IsKeyboardUsabilityExperimentEnabled() {
   return CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kKeyboardUsabilityExperiment);
 }
 
+bool IsKeyboardOverscrollEnabled() {
+  if (!IsKeyboardEnabled())
+    return false;
+  // Users of the accessibility on-screen keyboard are likely to be using mouse
+  // input, which may interfere with overscrolling.
+  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 IsInputViewEnabled() {
   if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kEnableInputView))
     return true;
   if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kDisableInputView))
     return false;
   // Default value if no command line flags specified.
   return false;
 }
 
 bool InsertText(const base::string16& text, aura::Window* root_window) {
@@ skipping 205 matching lines @@
 }
 
 void LogKeyboardControlEvent(KeyboardControlEvent event) {
   UMA_HISTOGRAM_ENUMERATION(
       "VirtualKeyboard.KeyboardControlEvent",
       event,
       keyboard::KEYBOARD_CONTROL_MAX);
 }
 
 }  // namespace keyboard