Add glue between the client and engine for Blimp

blimp/common/proto/input.proto

Index: blimp/common/proto/input.proto
diff --git a/blimp/common/proto/input.proto b/blimp/common/proto/input.proto
index fa6fe62ea7d9bf45c1e67c138cffc5d7ea6530dc..7b9a4043f917c31ea814d5a87b997a3488401e4a 100644
--- a/blimp/common/proto/input.proto
+++ b/blimp/common/proto/input.proto
@@ -11,8 +11,6 @@ syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
-import "common.proto";
-
 package blimp;
 
 message GestureCommon {
@@ -78,6 +76,9 @@ message InputMessage {
 
   optional Type type = 1;
 
+  // An ID that corresponds to RenderWidgetMessage.render_widget_id.
+  optional uint32 render_widget_id = 10;
+
   // Seconds since client platform start (boot) with millisecond resolution.
   // On Android, this is based off of the client's SystemClock#uptimeMillis().
   optional double timestamp_seconds = 2;