Add the partial screen magnifier to Chrome OS.

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index b12343a251a71d5a2555e9e8ad397123fdf0fb17..07100c6c857ff0310c3689d38d480cba07f1d51f 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -729,10 +729,10 @@ const char kLanguageXkbAutoRepeatInterval[] =
 const char kSpokenFeedbackEnabled[] = "settings.accessibility";
 // A boolean pref which determines whether high conrast is enabled.
 const char kHighContrastEnabled[] = "settings.a11y.high_contrast_enabled";
-// A boolean pref which determines whether screen magnifier is enabled.
-const char kScreenMagnifierEnabled[] = "settings.a11y.screen_magnifier";
 // A double pref which determines a zooming scale of the screen magnifier.
 const char kScreenMagnifierScale[] = "settings.a11y.screen_magnifier_scale";
+// A string pref which determines what type of screen magnifier is enabled.
+const char kScreenMagnifierType[] = "settings.a11y.screen_magnifier_type";
 // A boolean pref which determines whether virtual keyboard is enabled.
 // TODO(hashimoto): Remove this pref.
 const char kVirtualKeyboardEnabled[] = "settings.a11y.virtual_keyboard";