Move quic_flags.h from net/quic/core to net/quic/platform and split into api and impl.

net/quic/core/quic_versions.cc

Index: net/quic/core/quic_versions.cc
diff --git a/net/quic/core/quic_versions.cc b/net/quic/core/quic_versions.cc
index 2c8d9eae66c69fbdd73bfe93294dda32d5fdc05b..b94997dd4ef05fda6da005a531162ea1aa01e40b 100644
--- a/net/quic/core/quic_versions.cc
+++ b/net/quic/core/quic_versions.cc
@@ -5,9 +5,9 @@
 #include "net/quic/core/quic_versions.h"
 
 #include "net/quic/core/quic_error_codes.h"
-#include "net/quic/core/quic_flags.h"
 #include "net/quic/core/quic_tag.h"
 #include "net/quic/core/quic_types.h"
+#include "net/quic/platform/api/quic_flags.h"
 #include "net/quic/platform/api/quic_logging.h"
 
 using std::string;
@@ -31,7 +31,7 @@ QuicVersionVector FilterSupportedVersions(QuicVersionVector versions) {
   filtered_versions.clear();  // Guaranteed by spec not to change capacity.
   for (QuicVersion version : versions) {
     if (version == QUIC_VERSION_39) {
-      if (base::GetFlag(FLAGS_quic_enable_version_39) &&
+      if (GetQuicFlag(FLAGS_quic_enable_version_39) &&
           FLAGS_quic_reloadable_flag_quic_enable_version_38) {
         filtered_versions.push_back(version);
       }