relnote: Inline all frames smaller than a pointer into QuicFrame.

net/quic/quic_protocol.h

Index: net/quic/quic_protocol.h
diff --git a/net/quic/quic_protocol.h b/net/quic/quic_protocol.h
index eb80b7d39b710df8184ede173fcf97aa370d4132..b524aa40c429a46ea0878459669cc2837a92dfe6 100644
--- a/net/quic/quic_protocol.h
+++ b/net/quic/quic_protocol.h
@@ -690,13 +690,11 @@ enum QuicVersionNegotiationState {
 typedef QuicPacketPublicHeader QuicVersionNegotiationPacket;
 
 // A padding frame contains no payload.
-struct NET_EXPORT_PRIVATE QuicPaddingFrame {
-};
+struct NET_EXPORT_PRIVATE QuicPaddingFrame {};
 
 // A ping frame contains no payload, though it is retransmittable,
 // and ACK'd just like other normal frames.
-struct NET_EXPORT_PRIVATE QuicPingFrame {
-};
+struct NET_EXPORT_PRIVATE QuicPingFrame {};
 
 // A path MTU discovery frame contains no payload and is serialized as a ping
 // frame.
@@ -999,39 +997,43 @@ enum EncryptionLevel {
 
 struct NET_EXPORT_PRIVATE QuicFrame {
   QuicFrame();
-  explicit QuicFrame(QuicPaddingFrame* padding_frame);
+  explicit QuicFrame(QuicPaddingFrame padding_frame);
+  explicit QuicFrame(QuicMtuDiscoveryFrame frame);
+  explicit QuicFrame(QuicPingFrame frame);
+  explicit QuicFrame(QuicBlockedFrame frame);
+
   explicit QuicFrame(QuicStreamFrame* stream_frame);
   explicit QuicFrame(QuicAckFrame* frame);
-  explicit QuicFrame(QuicMtuDiscoveryFrame* frame);
-
   explicit QuicFrame(QuicRstStreamFrame* frame);
   explicit QuicFrame(QuicConnectionCloseFrame* frame);
   explicit QuicFrame(QuicStopWaitingFrame* frame);
-  explicit QuicFrame(QuicPingFrame* frame);
   explicit QuicFrame(QuicGoAwayFrame* frame);
   explicit QuicFrame(QuicWindowUpdateFrame* frame);
-  explicit QuicFrame(QuicBlockedFrame* frame);
 
   NET_EXPORT_PRIVATE friend std::ostream& operator<<(
       std::ostream& os, const QuicFrame& frame);
 
   QuicFrameType type;
   union {
-    QuicPaddingFrame* padding_frame;
+    // Frames smaller than a pointer are inline.
+    QuicPaddingFrame padding_frame;
+    QuicMtuDiscoveryFrame mtu_discovery_frame;
+    QuicPingFrame ping_frame;
+    QuicBlockedFrame blocked_frame;
+
+    // Frames larger than a pointer.
     QuicStreamFrame* stream_frame;
     QuicAckFrame* ack_frame;
-    QuicMtuDiscoveryFrame* mtu_discovery_frame;
-
     QuicStopWaitingFrame* stop_waiting_frame;
-
-    QuicPingFrame* ping_frame;
     QuicRstStreamFrame* rst_stream_frame;
     QuicConnectionCloseFrame* connection_close_frame;
     QuicGoAwayFrame* goaway_frame;
     QuicWindowUpdateFrame* window_update_frame;
-    QuicBlockedFrame* blocked_frame;
   };
 };
+// QuicFrameType consumes 8 bytes with padding.
+static_assert(sizeof(QuicFrame) <= 16,
+              "Frames larger than 8 bytes should be referenced by pointer.");
 
 typedef std::vector<QuicFrame> QuicFrames;