Add new certificateProvider extension API.

net/ssl/ssl_platform_key.h

Index: net/ssl/ssl_platform_key.h
diff --git a/net/ssl/ssl_platform_key.h b/net/ssl/ssl_platform_key.h
index bcab6a4c32d0c9b355fe364915ca1095fb4eba89..54d4f494e56a6fbb4b37bf1d4465bbc74a24d590 100644
--- a/net/ssl/ssl_platform_key.h
+++ b/net/ssl/ssl_platform_key.h
@@ -7,6 +7,7 @@
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "net/base/net_export.h"
 
 namespace base {
 class SequencedTaskRunner;
@@ -17,6 +18,11 @@ namespace net {
 class SSLPrivateKey;
 class X509Certificate;
 
+using FetchPrivateKeyFunc =
+    scoped_ptr<SSLPrivateKey>(X509Certificate* certificate);
+
+NET_EXPORT extern FetchPrivateKeyFunc* fetch_private_key_func;
+
 // Looks up the private key from the platform key store corresponding to
 // |certificate|'s public key and returns an SSLPrivateKey which offloads
 // signing operations to |task_runner|. |task_runner| is a SequencedTaskRunner