Add Chrome OS accessibility histograms.

content/browser/accessibility/browser_accessibility_state_impl.h

Index: content/browser/accessibility/browser_accessibility_state_impl.h
diff --git a/content/browser/accessibility/browser_accessibility_state_impl.h b/content/browser/accessibility/browser_accessibility_state_impl.h
index fd2bd39e61990961d81f1de784663f8d817ce741..40d99fd409f24be80fd7ee7bb5aca25ae2dc143e 100644
--- a/content/browser/accessibility/browser_accessibility_state_impl.h
+++ b/content/browser/accessibility/browser_accessibility_state_impl.h
@@ -5,6 +5,8 @@
 #ifndef CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_
 #define CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_
 
+#include <vector>
+
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/singleton.h"
@@ -41,6 +43,7 @@ class CONTENT_EXPORT BrowserAccessibilityStateImpl
   virtual void OnAccessibilityEnabledManually() OVERRIDE;
   virtual void OnScreenReaderDetected() OVERRIDE;
   virtual bool IsAccessibleBrowser() OVERRIDE;
+  virtual void AddHistogramCallback(base::Closure callback) OVERRIDE;
 
   // Called a short while after startup to allow time for the accessibility
   // state to be determined. Updates a histogram with the current state.
@@ -60,6 +63,8 @@ class CONTENT_EXPORT BrowserAccessibilityStateImpl
 
   AccessibilityMode accessibility_mode_;
 
+  std::vector<base::Closure> histogram_callbacks_;
+
   DISALLOW_COPY_AND_ASSIGN(BrowserAccessibilityStateImpl);
 };