Revert of Migrate tsmon protos to proto3

common/tsmon/ts_mon_proto/metrics.proto

Index: common/tsmon/ts_mon_proto/metrics.proto
diff --git a/common/tsmon/ts_mon_proto/metrics.proto b/common/tsmon/ts_mon_proto/metrics.proto
index 3842b236e846d4faf27bdb0adbf8478e7e727b33..8ff72e50fd671e85f3d071785cd3a20cf60167c2 100644
--- a/common/tsmon/ts_mon_proto/metrics.proto
+++ b/common/tsmon/ts_mon_proto/metrics.proto
@@ -4,7 +4,7 @@
 
 // Copied from https://chromium.googlesource.com/infra/infra/+/master/infra_libs/ts_mon/protos/
 
-syntax = "proto3";
+syntax = "proto2";
 
 package ts_mon.proto;
 
@@ -14,29 +14,28 @@
 message MetricsCollection {
   repeated MetricsData data = 1;
 
-  uint64 start_timestamp_us = 2;
-  string collection_point_id = 3;
+  optional uint64 start_timestamp_us = 2;
+  optional string collection_point_id = 3;
 }
 
 message MetricsField {
-  string name = 1;
+  optional string name = 1;
 
-  FieldType type = 3;
+  optional FieldType type = 3 [default = STRING];
   enum FieldType {
-    UNKNOWN = 0;
     STRING = 1;
     INT = 2;
     BOOL = 3;
   };
 
-  string string_value = 4;
-  int64 int_value = 5;
-  bool bool_value = 6;
+  optional string string_value = 4;
+  optional int64 int_value = 5;
+  optional bool bool_value = 6;
 }
 
 message PrecomputedDistribution {
   enum SpecType {
-    UNKNOWN = 0;
+
     CANONICAL_POWERS_OF_2 = 1;
     CANONICAL_POWERS_OF_10_P_0_2 = 2;
     CANONICAL_POWERS_OF_10 = 3;
@@ -44,37 +43,37 @@
     CUSTOM_BOUNDED = 21;
   }
 
-  SpecType spec_type = 1;
-  double width = 2;
-  double growth_factor = 3;
-  int32 num_buckets = 4;
+  optional SpecType spec_type = 1;
+  optional double width = 2 [default = 10.0];
+  optional double growth_factor = 3 [default = 0.0];
+  optional int32 num_buckets = 4 [default = 10];
   repeated double lower_bounds = 5;
-  bool is_cumulative = 6;
+  optional bool is_cumulative = 6 [default = false];
   repeated sint64 bucket = 7;
-  sint64 underflow = 8;
-  sint64 overflow = 9;
-  double mean = 10;
-  double sum_of_squared_deviation = 11;
+  optional sint64 underflow = 8;
+  optional sint64 overflow = 9;
+  optional double mean = 10;
+  optional double sum_of_squared_deviation = 11;
 }
 
 message MetricsData {
-  string name = 1;  // Required.
-  string metric_name_prefix = 2;
+  required string name = 1;
+  optional string metric_name_prefix = 2;
 
-  ts_mon.proto.NetworkDevice network_device = 11;
-  ts_mon.proto.Task task = 12;
+  optional ts_mon.proto.NetworkDevice network_device = 11;
+  optional ts_mon.proto.Task task = 12;
 
   repeated MetricsField fields = 20;
 
-  int64 counter = 30;
-  int64 gauge = 32;
-  double noncumulative_double_value = 34;
-  PrecomputedDistribution distribution = 35;
-  string string_value = 36;
-  bool boolean_value = 37;
-  double cumulative_double_value = 38;
+  optional int64 counter = 30;
+  optional int64 gauge = 32;
+  optional double noncumulative_double_value = 34;
+  optional PrecomputedDistribution distribution = 35;
+  optional string string_value = 36;
+  optional bool boolean_value = 37;
+  optional double cumulative_double_value = 38;
 
-  uint64 start_timestamp_us = 40;
+  optional uint64 start_timestamp_us = 40;
 
   enum Units {
     UNKNOWN_UNITS = 0;
@@ -105,7 +104,7 @@
     MILLIAMPS = 61;
     DEGREES_CELSIUS = 62;
   }
-  Units units = 41;
+  optional Units units = 41;
 
-  string description = 43;
+  optional string description = 43;
 }