Add various UMA histograms for measuring GCM crypto performance

components/gcm_driver/gcm_driver.h

Index: components/gcm_driver/gcm_driver.h
diff --git a/components/gcm_driver/gcm_driver.h b/components/gcm_driver/gcm_driver.h
index 12445a8811aaa00f959338f192498cd10924092e..c33890a3636664662d9f28d563aa4b26febb2161 100644
--- a/components/gcm_driver/gcm_driver.h
+++ b/components/gcm_driver/gcm_driver.h
@@ -260,7 +260,7 @@ class GCMDriver {
   // Platform-specific implementation of recording message decryption failures.
   virtual void RecordDecryptionFailure(
       const std::string& app_id,
-      GCMEncryptionProvider::DecryptionFailure reason) = 0;
+      GCMEncryptionProvider::DecryptionResult result) = 0;
 
   // Runs the Register callback.
   void RegisterFinished(const std::string& app_id,
@@ -298,6 +298,13 @@ class GCMDriver {
                           const std::string* sender_id,
                           const UnregisterCallback& callback);
 
+  // Dispatches the OnMessage event to the app handler associated with |app_id|
+  // if |result| indicates that it is safe to do so, or will report a decryption
+  // failure for the |app_id| otherwise.
+  void DispatchMessageInternal(const std::string& app_id,
+                               GCMEncryptionProvider::DecryptionResult result,
+                               const IncomingMessage& message);
+
   // Called after unregistration completes in order to trigger the pending
   // registration.
   void RegisterAfterUnregister(