Add test for accessibility histograms.

content/public/browser/browser_accessibility_state.h

Index: content/public/browser/browser_accessibility_state.h
diff --git a/content/public/browser/browser_accessibility_state.h b/content/public/browser/browser_accessibility_state.h
index 4c89f5aa6930afbb8eac7429c33982f6d84ef34b..269f77b4247fc22a85ad3b001353ff1274611c25 100644
--- a/content/public/browser/browser_accessibility_state.h
+++ b/content/public/browser/browser_accessibility_state.h
@@ -34,6 +34,9 @@ class CONTENT_EXPORT BrowserAccessibilityState {
   // Use this to register a method to update additional accessibility
   // histograms.
   virtual void AddHistogramCallback(base::Closure callback) = 0;
+
+  // This method is only for testing!
+  virtual void UpdateHistograms() = 0;

[Jói, 2013/01/08 20:44:59]

I was going to tell you to name it UpdateHistogramsForTesting, until I saw the
comment in browser_accessibility_state_impl.h, that it's _public_ only for
testing, otherwise would presumably be private.

I think the method exposed in the API (and publicly on
BrowserAccessibilityStateImpl) should be named UpdateHistogramsForTesting.  It
could turn around and call UpdateHistograms which would be private.

 };
 
 }  // namespace content