Re-implement PageState serialization without a Blink API dependency.

base/strings/nullable_string16.cc

Index: base/strings/nullable_string16.cc
diff --git a/base/debug/trace_event_impl_constants.cc b/base/strings/nullable_string16.cc
similarity index 44%
copy from base/debug/trace_event_impl_constants.cc
copy to base/strings/nullable_string16.cc
index 71e9e08db78ee843c482792d65fbe8c89ed28e64..740147b092ff13ec258cc39787041d3099b35cab 100644
--- a/base/debug/trace_event_impl_constants.cc
+++ b/base/strings/nullable_string16.cc
@@ -2,13 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "base/debug/trace_event_impl.h"
+#include "base/nullable_string16.h"
+
+#include <ostream>
+
+#include "base/strings/utf_string_conversions.h"
 
 namespace base {
-namespace debug {
 
-// Enable everything but debug and test categories by default.
-const char* CategoryFilter::kDefaultCategoryFilterString = "-*Debug,-*Test";
+std::ostream& operator<<(std::ostream& out, const NullableString16& value) {
+  return value.is_null() ? out << "(null)" : out << UTF16ToUTF8(value.string());
+}
 
-}  // namespace debug
 }  // namespace base