Teach the GCM Driver how to decrypt incoming messages.

components/gcm_driver/crypto/gcm_encryption_provider.h

Index: components/gcm_driver/crypto/gcm_encryption_provider.h
diff --git a/components/gcm_driver/crypto/gcm_encryption_provider.h b/components/gcm_driver/crypto/gcm_encryption_provider.h
index fce5732b0c64bd9c5f57c6fa5587b546a9d9b212..e4cff8dc1d0378af8f656eaa653463eb36ef68eb 100644
--- a/components/gcm_driver/crypto/gcm_encryption_provider.h
+++ b/components/gcm_driver/crypto/gcm_encryption_provider.h
@@ -20,7 +20,10 @@ class SequencedTaskRunner;
 
 namespace gcm {
 
+struct EncryptionHeaderValue;
+struct EncryptionKeyHeaderValue;
 class GCMKeyStore;
+struct IncomingMessage;
 class KeyPair;
 
 // Provider that enables the GCM Driver to deal with encryption key management
@@ -30,6 +33,10 @@ class GCMEncryptionProvider {
   // Callback to be invoked when the public encryption key is available.
   using PublicKeyCallback = base::Callback<void(const std::string&)>;
 
+  // Callback to be invoked when a message may have been decrypted.
+  using MessageCallback =
+      base::Callback<void(const IncomingMessage&, bool decryption_successful)>;
+
   GCMEncryptionProvider();
   ~GCMEncryptionProvider();
 
@@ -45,6 +52,15 @@ class GCMEncryptionProvider {
   void GetPublicKey(const std::string& app_id,
                     const PublicKeyCallback& callback);
 
+  // Determines whether |message| contains encrypted content.
+  bool IsEncryptedMessage(const IncomingMessage& message) const;
+
+  // Decrypts |message| and stores the result in |decrypted_message|. The return
+  // value indicates whether the message could be decrypted successfully.
+  void DecryptMessage(const std::string& app_id,
+                      const IncomingMessage& message,
+                      const MessageCallback& callback);
+
  private:
   void DidGetPublicKey(const std::string& app_id,
                        const PublicKeyCallback& callback,
@@ -53,6 +69,14 @@ class GCMEncryptionProvider {
   void DidCreatePublicKey(const PublicKeyCallback& callback,
                           const KeyPair& pair);
 
+  void DecryptMessageWithKey(
+      const IncomingMessage& message,
+      const MessageCallback& callback,
+      const EncryptionHeaderValue& encryption_header,
+      const EncryptionKeyHeaderValue& encryption_key_header,
+      const std::string& ciphertext,
+      const KeyPair& pair);
+
   scoped_refptr<GCMKeyStore> key_store_;
 
   base::WeakPtrFactory<GCMEncryptionProvider> weak_ptr_factory_;