Tracing V2: Fully-functional plugin.

components/tracing/core/proto_zero_message.h

Index: components/tracing/core/proto_zero_message.h
diff --git a/components/tracing/core/proto_zero_message.h b/components/tracing/core/proto_zero_message.h
index b5b0a37cce1bc4b82788c62108ee7036702cb6d0..ecf6cec747378891dcc5dd7bebc4ade2634afb7a 100644
--- a/components/tracing/core/proto_zero_message.h
+++ b/components/tracing/core/proto_zero_message.h
@@ -7,6 +7,7 @@
 
 #include <stdint.h>
 
+#include <set>
 #include <type_traits>
 
 #include "base/compiler_specific.h"
@@ -62,7 +63,7 @@ class TRACING_EXPORT ProtoZeroMessage {
  protected:
   ProtoZeroMessage();
 
-  // Proto types: uint64, uint32, int64, int32, bool, enum.
+  // Proto types: uint64, uint32, int64, int32, enum (large).
   template <typename T>
   void AppendVarInt(uint32_t field_id, T value) {
     if (nested_message_)
@@ -83,6 +84,21 @@ class TRACING_EXPORT ProtoZeroMessage {
     AppendVarInt(field_id, proto::ZigZagEncode(value));
   }
 
+  // Proto types: bool, enum (small).
+  // Faster version of AppendVarInt for tiny numbers.
+  void AppendTinyVarInt(uint32_t field_id, int32_t value) {
+    DCHECK(0 <= value && value < 0x80);
+    if (nested_message_)
+      EndNestedMessage();
+
+    uint8_t buffer[proto::kMaxSimpleFieldEncodedSize];
+    uint8_t* pos = buffer;
+    // MakeTagVarInt gets super optimized here for constexpr.
+    pos = proto::WriteVarInt(proto::MakeTagVarInt(field_id), pos);
+    *pos++ = static_cast<uint8_t>(value);
+    WriteToStream(buffer, pos);
+  }
+
   // Proto types: fixed64, sfixed64, fixed32, sfixed32, double, float.
   template <typename T>
   void AppendFixed(uint32_t field_id, T value) {
@@ -99,7 +115,6 @@ class TRACING_EXPORT ProtoZeroMessage {
     WriteToStream(buffer, pos);
   }
 
-  // TODO(kraynov): Add AppendTinyInt.
   void AppendString(uint32_t field_id, const char* str);
   void AppendBytes(uint32_t field_id, const void* value, size_t size);