tracing v2: Introduce TraceBufferWriter

components/tracing/core/proto_utils.h

Index: components/tracing/core/proto_utils.h
diff --git a/components/tracing/core/proto_utils.h b/components/tracing/core/proto_utils.h
index 68599199688e98f0182aeb874a4e6e15e0585f2d..dfa983e0297c599c9dfda0a3690ef1ab6ae39842 100644
--- a/components/tracing/core/proto_utils.h
+++ b/components/tracing/core/proto_utils.h
@@ -95,6 +95,12 @@ void WriteRedundantVarIntU32(uint32_t value, uint8_t* buf) {
   DCHECK_EQ(0u, value) << "Buffer too short to encode the given value";
 }
 
+template <uint32_t field_id>
+void StaticAssertSingleBytePreamble() {
+  static_assert(field_id < 16,
+                "Proto field id too big to fit in a single byte preamble");
+};
+
 }  // namespace proto
 }  // namespace v2
 }  // namespace tracing