Implement overscroll support for the virtual keyboard.

ui/keyboard/keyboard_switches.h

Index: ui/keyboard/keyboard_switches.h
diff --git a/ui/keyboard/keyboard_switches.h b/ui/keyboard/keyboard_switches.h
index 04d4e73702450a7e1155dea3423f601ad55ddae7..bc0ae1b05279a9de001c74dc42ed4b1ba9dc6250 100644
--- a/ui/keyboard/keyboard_switches.h
+++ b/ui/keyboard/keyboard_switches.h
@@ -10,12 +10,21 @@
 namespace keyboard {
 namespace switches {
 
+// Disabled overscrolling of web content when the virtual keyboard is displayed.
+// If disabled, the work area is resized to restrict windows from overlapping
+// with the keybaord area.
+KEYBOARD_EXPORT extern const char kDisableVirtualKeyboardOverscroll[];
+
 // Enables the swipe selection feature on the virtual keyboard.
 KEYBOARD_EXPORT extern const char kEnableSwipeSelection[];
 
 // Enables the virtual keyboard.
 KEYBOARD_EXPORT extern const char kEnableVirtualKeyboard[];
 
+// Enable overscrolling of web content when the virtual keyboard is displayed
+// to provide access to content that would otherwise be occluded.
+KEYBOARD_EXPORT extern const char kEnableVirtualKeyboardOverscroll[];
+
 // Enables the keyboard usability experiment. This is an experimental mode for
 // testing the usability of various experimental keyboard layouts.
 KEYBOARD_EXPORT extern const char kKeyboardUsabilityExperiment[];