certificate manager: Disable export option for TPM-backed certs.

chrome/browser/certificate_manager_model.h

Index: chrome/browser/certificate_manager_model.h
diff --git a/chrome/browser/certificate_manager_model.h b/chrome/browser/certificate_manager_model.h
index a82409483dcc1b2cee818ec32f68ece448cc07a7..f00a5cb6a944641dc0c691937d02b2fc10e89f64 100644
--- a/chrome/browser/certificate_manager_model.h
+++ b/chrome/browser/certificate_manager_model.h
@@ -100,6 +100,9 @@ class CertificateManagerModel {
   // function returns.
   bool Delete(net::X509Certificate* cert);
 
+  // IsHardwareBacked returns true if |cert| is hardware backed.

[wtc, 2012/05/22 23:43:46]

Please document that this function is only implemented for
Chrome OS and always returns false on other platforms.

[hshi1, 2012/05/23 00:03:29]

Done.

+  bool IsHardwareBacked(const net::X509Certificate* cert) const;
+
  private:
   // Callback used by Refresh() for when the cert slots have been unlocked.
   // This method does the actual refreshing.