Add the partial screen magnifier to Chrome OS.

chrome/browser/chromeos/accessibility/accessibility_util.h

Index: chrome/browser/chromeos/accessibility/accessibility_util.h
diff --git a/chrome/browser/chromeos/accessibility/accessibility_util.h b/chrome/browser/chromeos/accessibility/accessibility_util.h
index e85d3dd7b09764818e85e93a8427f7b39fc42744..a3cc3a705dde13a8b2771749b55c8a89d1cffa9e 100644
--- a/chrome/browser/chromeos/accessibility/accessibility_util.h
+++ b/chrome/browser/chromeos/accessibility/accessibility_util.h
@@ -23,8 +23,14 @@ void EnableSpokenFeedback(bool enabled, content::WebUI* login_web_ui);
 // Enable or disable the high contrast mode for Chrome.
 void EnableHighContrast(bool enabled);
 
-// Enable or disable the screen magnifier.
-void EnableScreenMagnifier(bool enabled);
+enum ScreenMagnifierType {
+  MagnifierNone,
+  MagnifierFull,
+  MagnifierPartial,
+};
+
+// Set the type of screen magnifier, or disable it.
+void SetScreenMagnifier(ScreenMagnifierType type);
 
 // Enable or disable the virtual keyboard.
 void EnableVirtualKeyboard(bool enabled);
@@ -42,8 +48,8 @@ bool IsSpokenFeedbackEnabled();
 // Returns true if High Contrast is enabled, or false if not.
 bool IsHighContrastEnabled();
 
-// Returns true if Screen Magnifier is enabled, or false if not.
-bool IsScreenMagnifierEnabled();
+// Returns the current state of the screen magnifier.
+ScreenMagnifierType GetScreenMagnifierType();
 
 // Speak the given text if the accessibility pref is already set.
 void MaybeSpeak(const std::string& utterance);