Add support for variations controlled overriding UI strings to the variations service.

components/variations/proto/study.proto

Index: components/variations/proto/study.proto
diff --git a/components/variations/proto/study.proto b/components/variations/proto/study.proto
index e58b8f9092aa78dc3f67347930048557cb9b6c52..24c8bee04bdebc57196894f3a9aa8926ed3bdb42 100644
--- a/components/variations/proto/study.proto
+++ b/components/variations/proto/study.proto
@@ -43,7 +43,7 @@ message Study {
 
   // An experiment within the study.
   //
-  // Next tag: 9
+  // Next tag: 10
   message Experiment {
     // A named parameter value for this experiment.
     //
@@ -107,6 +107,19 @@ message Study {
       KILL_CRITICAL = 3;
     }
     optional Type type = 7 [default = NORMAL];
+
+    // A UI string to override, and the new value to use.
+    message OverrideUIString {
+      // The first 32 bits of the MD5 hash digest of the resource name to
+      // override.
+      // e.g. Hash("IDS_BOOKMARK_BAR_UNDO")
+      optional fixed32 name_hash = 1;
+
+      // The new value of the string being overridden.
+      // e.g. "Undo"
+      optional string value = 2;
+    }
+    repeated OverrideUIString override_ui_string = 9;
   }
 
   // List of experiments in this study. This list should include the default /