Fix comments about HTTP2 GREASE Frames

Update two comments about the behavior of the http2-grease-frame-type
feature to better describe exactly what it does.

Change-Id: I2b5269a3117a499067f111fa25cacd5cc067f0ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2209606
Auto-Submit: Eric Lawrence [MSFT] <ericlaw@microsoft.com>
Reviewed-by: Bence Béky <bnc@chromium.org>
Commit-Queue: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770892}

net/http/http_network_session.h

@@ -115,7 +115,7 @@ class NET_EXPORT HttpNetworkSession {
     // logic from hiding broken servers.
     spdy::SettingsMap http2_settings;
     // If set, an HTTP/2 frame with a reserved frame type will be sent after
-    // every HEADERS and SETTINGS frame.  See
+    // every HTTP/2 SETTINGS frame and before every HTTP/2 DATA frame.
     // https://tools.ietf.org/html/draft-bishop-httpbis-grease-00.
     // The same frame will be sent out on all connections to prevent the retry
     // logic from hiding broken servers.

net/spdy/spdy_session.h

@@ -1106,8 +1106,8 @@ class NET_EXPORT SpdySession : public BufferedSpdyFramerVisitorInterface,
   // and maximum HPACK dynamic table size.
   const spdy::SettingsMap initial_settings_;
 
-  // If set, an HTTP/2 frame with a reserved frame type will be sent after every
-  // valid HTTP/2 frame.  See
+  // If set, an HTTP/2 frame with a reserved frame type will be sent after
+  // every HTTP/2 SETTINGS frame and before every HTTP/2 DATA frame. See
   // https://tools.ietf.org/html/draft-bishop-httpbis-grease-00.
   const base::Optional<SpdySessionPool::GreasedHttp2Frame> greased_http2_frame_;