[package.proto] convert deps from list to map.

recipe_engine/package.proto

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 // Recompile with protoc 3.1.0+:
 // cd recipe_engine && protoc package.proto --python_out=.
 
 syntax = "proto3";
 
 package recipe_engine;
 
 message DepSpec {
-  // Same meaning as Package.project_id, but the id for this dependency. This
-  // should always match the project_id of the repo that we're depending on.
-  string project_id = 1;
-
   // The URL of where to fetch the package data. Must always be a git repo URL.
-  string url = 2;
+  string url = 1;
 
   // The ref to git-fetch when syncing this dependency.
-  string branch = 3;
+  string branch = 2;
 
   // The git commit that we depend on.
-  string revision = 4;
+  string revision = 3;
 
   // Treat a subtree of a repo as a whole repo unto itself. This must match
   // the value of `recipes_path` in the target repo.
-  string path_override = 5;
+  string path_override = 4;
 
   enum RepoType {
     // Do a full 'git clone' of this dependency.
     GIT = 0;
 
     // Use GITILES to fetch the dependency data via the GITILES REST API.
     GITILES = 1;
   }
   // How this dependency should be fetched.
   //
   // NOTE: this option may be removed in the future in preference for
   // automatically picking the repo fetch method.
-  RepoType repo_type = 6;
+  RepoType repo_type = 5;
 }
 
 // These options control the behavior of the autoroller recipe:
 //   https://chromium.googlesource.com/infra/infra/+/master/recipes/recipes/recipe_autoroller.py
 message AutorollRecipeOptions {
   // These control the behavior of the autoroller when it finds a trivial roll
   // (i.e. a roll without expectation changes).
   message TrivialOptions {
     // These email addresses will be TBR'd.
     repeated string tbr_emails = 1;
@@ skipping 33 matching lines @@
 
   // This is the URL which points to the 'source of truth' for this repo. It's
   // meant to be used for documentation generation.
   string canonical_repo_url = 3;
 
   // The path (using forward slashes) to where the base of the recipes are found
   // in the repo (i.e. where the "recipes" and/or "recipe_modules" directories
   // live).
   string recipes_path = 4;
 
-  // Any package dependencies that this package has.
-  repeated DepSpec deps = 5;
+  // A mapping of a dependency ("project_id") to spec needed to fetch its code.
+  map<string, DepSpec> deps = 5;
 
   // The autoroller options for this repo. These options will be respected by
   // the autoroller recipe (which currently lives here:
   //   https://chromium.googlesource.com/infra/infra/+/master/recipes/recipes/recipe_autoroller.py
   // ).
   AutorollRecipeOptions autoroll_recipe_options = 6;
-
 }