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 0f827815b18ecaab7cc5c48a1fa694866f734262..d835b5e42ab1b4bbe1e96b7ffb86cb74b2b2f110 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -694,6 +694,8 @@ const char kSpokenFeedbackEnabled[] = "settings.accessibility";
 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 boolean pref which determines whether the partial magnifier is enabled.
+const char kPartialScreenMagnifierEnabled[] = "settings.a11y.partial_magnifier";
 // A boolean pref which determines whether virtual keyboard is enabled.
 // TODO(hashimoto): Remove this pref.
 const char kVirtualKeyboardEnabled[] = "settings.a11y.virtual_keyboard";