Break ChannelIDSigner into two classes: ChannelIDKey and ChannelIDSource.

net/tools/quic/quic_client.h

Index: net/tools/quic/quic_client.h
diff --git a/net/tools/quic/quic_client.h b/net/tools/quic/quic_client.h
index 5568b1efa6b2837eeb0b12c6cd41516d8a4ae755..e1b1c2d86cbbd11ae318f9744142ef6e1b509e25 100644
--- a/net/tools/quic/quic_client.h
+++ b/net/tools/quic/quic_client.h
@@ -152,11 +152,12 @@ class QuicClient : public EpollCallbackInterface,
     crypto_config_.SetProofVerifier(verifier);
   }
 
-  // SetChannelIDSigner sets a ChannelIDSigner that will be called when the
-  // server supports channel IDs to sign a message proving possession of the
-  // given ChannelID. This object takes ownership of |signer|.
-  void SetChannelIDSigner(ChannelIDSigner* signer) {
-    crypto_config_.SetChannelIDSigner(signer);
+  // SetChannelIDSource sets a ChannelIDSource that will be called, when the
+  // server supports channel IDs, to obtain a channel ID for signing a message
+  // proving possession of the channel ID. This object takes ownership of
+  // |source|.
+  void SetChannelIDSource(ChannelIDSource* source) {
+    crypto_config_.SetChannelIDSource(source);
   }
 
   void SetSupportedVersions(const QuicVersionVector& versions) {