Initial translation event proto.

components/sync/protocol/user_event_specifics.proto

Index: components/sync/protocol/user_event_specifics.proto
diff --git a/components/sync/protocol/user_event_specifics.proto b/components/sync/protocol/user_event_specifics.proto
index d02b2833eb7ca9db5b8859bb587a5b799e961b5b..ae3d5c52afb252934ce33bc1466967ddfd00d542 100644
--- a/components/sync/protocol/user_event_specifics.proto
+++ b/components/sync/protocol/user_event_specifics.proto
@@ -39,6 +39,23 @@ message LanguageDetection {
   optional string adopted_language = 2;
 }
 
+// User translated a page or interacted with translate suggestion.
+message Translation {
+  optional string from_language_code = 1;

[amoylan, 2017/05/26 05:12:42]

We need a comment on these fields (from_language_code, to_language_code).
Actually I think we need a somewhat detailed comment  here, because I feel like
they can have a different meaning (or no meaning) depending on the value of
Interaction enum.

For example, if interaction == MANUAL, will the from_ and to_ be the previous
auto-chosen values? Or the updated values? Or maybe exactly one of the from_ and
to_ will be set, indicating which one the user did manually enter?

[renjieliu1, 2017/05/29 00:09:50]

Done.

+  optional string to_language_code = 2;
+  enum Interaction {
+    UNKNOWN = 0;
+    ACCEPTED = 1;
+    REJECTED = 2;
+    IGNORED = 3;
+    DISMISSED = 4;
+    MANUAL = 5;  // User manually entered either language.
+    ALWAYS_TRANSLATE = 6;
+    NEVER_TRANSLATE = 7;
+  }
+  optional Interaction interaction = 3;
+}
+
 message UserEventSpecifics {
   // Time of event, as measured on the client (unix epoch).
   optional int64 event_time_usec = 1;
@@ -53,5 +70,6 @@ message UserEventSpecifics {
   oneof event {
     FieldTrialEvent field_trial_event = 4;
     LanguageDetection language_detection = 5;
+    Translation translation = 6;
   }
 }