Move GCMDecryptionResult to its own file

It's used in places beyond the GCMEncryptionProvider now, and might be
exposed to GCM app handlers in the future, so let's factor it out.

BUG=678347

Change-Id: I2301c05b403a4ec52d04e45616988ff40f270fde
Reviewed-on: https://chromium-review.googlesource.com/550155
Commit-Queue: Peter Beverloo <[email protected]>
Reviewed-by: Anita Woodruff <[email protected]>
Cr-Commit-Position: refs/heads/master@{#482657}
diff --git a/components/gcm_driver/gcm_client_impl.h b/components/gcm_driver/gcm_client_impl.h
index 62c4d3b..68c9e2e4 100644
--- a/components/gcm_driver/gcm_client_impl.h
+++ b/components/gcm_driver/gcm_client_impl.h
@@ -125,8 +125,7 @@
             const std::string& receiver_id,
             const OutgoingMessage& message) override;
   void RecordDecryptionFailure(const std::string& app_id,
-                               GCMEncryptionProvider::DecryptionResult result)
-      override;
+                               GCMDecryptionResult result) override;
   void SetRecording(bool recording) override;
   void ClearActivityLogs() override;
   GCMStatistics GetStatistics() const override;