Port cronet build rules to GN part 1

BUG=462737

Review URL: https://codereview.chromium.org/1483843002

Cr-Commit-Position: refs/heads/master@{#365357}
diff --git a/net/net.gyp b/net/net.gyp
index 6579e158..f18f434 100644
--- a/net/net.gyp
+++ b/net/net.gyp
@@ -81,7 +81,7 @@
     },
     {
       # Protobuf compiler / generator for QUIC crypto protocol buffer.
-      # GN version: //net/quic/proto
+      # GN version: //net:net_quic_proto
       'target_name': 'net_quic_proto',
       'type': 'static_library',
       'sources': [