Add plumbing for dry-run cherry-pick and revert

This passes the flag from ChangeService to Repository, which passes it
to Gitlab::Git, then to the Gitaly client, then to Gitaly. It defaults
to `false` at all points, maintaining existing behavior.

app/models/repository.rb

@@ -852,7 +852,7 @@ class Repository
 
   def revert(
     user, commit, branch_name, message,
-    start_branch_name: nil, start_project: project)
+    start_branch_name: nil, start_project: project, dry_run: false)
 
     with_cache_hooks do
       raw_repository.revert(
@@ -861,14 +861,15 @@ class Repository
         branch_name: branch_name,
         message: message,
         start_branch_name: start_branch_name,
-        start_repository: start_project.repository.raw_repository
+        start_repository: start_project.repository.raw_repository,
+        dry_run: dry_run
       )
     end
   end
 
   def cherry_pick(
     user, commit, branch_name, message,
-    start_branch_name: nil, start_project: project)
+    start_branch_name: nil, start_project: project, dry_run: false)
 
     with_cache_hooks do
       raw_repository.cherry_pick(
@@ -877,7 +878,8 @@ class Repository
         branch_name: branch_name,
         message: message,
         start_branch_name: start_branch_name,
-        start_repository: start_project.repository.raw_repository
+        start_repository: start_project.repository.raw_repository,
+        dry_run: dry_run
       )
     end
   end

app/services/commits/change_service.rb

@@ -22,7 +22,9 @@ module Commits
         @branch_name,
         message,
         start_project: @start_project,
-        start_branch_name: @start_branch)
+        start_branch_name: @start_branch,
+        dry_run: @dry_run
+      )
     rescue Gitlab::Git::Repository::CreateTreeError => ex
       act = action.to_s.dasherize
       type = @commit.change_type_title(current_user)

app/services/commits/create_service.rb

@@ -21,6 +21,7 @@ module Commits
       @start_sha = params[:start_sha]
       @branch_name = params[:branch_name]
       @force = params[:force] || false
+      @dry_run = params[:dry_run] || false
     end
 
     def execute

lib/gitlab/git/repository.rb

@@ -598,14 +598,15 @@ module Gitlab
         end
       end
 
-      def revert(user:, commit:, branch_name:, message:, start_branch_name:, start_repository:)
+      def revert(user:, commit:, branch_name:, message:, start_branch_name:, start_repository:, dry_run: false)
         args = {
           user: user,
           commit: commit,
           branch_name: branch_name,
           message: message,
           start_branch_name: start_branch_name,
-          start_repository: start_repository
+          start_repository: start_repository,
+          dry_run: dry_run
         }
 
         wrapped_gitaly_errors do
@@ -613,14 +614,15 @@ module Gitlab
         end
       end
 
-      def cherry_pick(user:, commit:, branch_name:, message:, start_branch_name:, start_repository:)
+      def cherry_pick(user:, commit:, branch_name:, message:, start_branch_name:, start_repository:, dry_run: false)
         args = {
           user: user,
           commit: commit,
           branch_name: branch_name,
           message: message,
           start_branch_name: start_branch_name,
-          start_repository: start_repository
+          start_repository: start_repository,
+          dry_run: dry_run
         }
 
         wrapped_gitaly_errors do

lib/gitlab/gitaly_client/operation_service.rb

@@ -187,24 +187,26 @@ module Gitlab
         raise Gitlab::Git::CommitError, e
       end
 
-      def user_cherry_pick(user:, commit:, branch_name:, message:, start_branch_name:, start_repository:)
+      def user_cherry_pick(user:, commit:, branch_name:, message:, start_branch_name:, start_repository:, dry_run: false)
         call_cherry_pick_or_revert(:cherry_pick,
                                    user: user,
                                    commit: commit,
                                    branch_name: branch_name,
                                    message: message,
                                    start_branch_name: start_branch_name,
-                                   start_repository: start_repository)
+                                   start_repository: start_repository,
+                                   dry_run: dry_run)
       end
 
-      def user_revert(user:, commit:, branch_name:, message:, start_branch_name:, start_repository:)
+      def user_revert(user:, commit:, branch_name:, message:, start_branch_name:, start_repository:, dry_run: false)
         call_cherry_pick_or_revert(:revert,
                                    user: user,
                                    commit: commit,
                                    branch_name: branch_name,
                                    message: message,
                                    start_branch_name: start_branch_name,
-                                   start_repository: start_repository)
+                                   start_repository: start_repository,
+                                   dry_run: dry_run)
       end
 
       def rebase(user, rebase_id, branch:, branch_sha:, remote_repository:, remote_branch:, push_options: [])
@@ -390,7 +392,7 @@ module Gitlab
         response
       end
 
-      def call_cherry_pick_or_revert(rpc, user:, commit:, branch_name:, message:, start_branch_name:, start_repository:)
+      def call_cherry_pick_or_revert(rpc, user:, commit:, branch_name:, message:, start_branch_name:, start_repository:, dry_run:)
         request_class = "Gitaly::User#{rpc.to_s.camelcase}Request".constantize
 
         request = request_class.new(
@@ -400,7 +402,8 @@ module Gitlab
           branch_name: encode_binary(branch_name),
           message: encode_binary(message),
           start_branch_name: encode_binary(start_branch_name.to_s),
-          start_repository: start_repository.gitaly_repository
+          start_repository: start_repository.gitaly_repository,
+          dry_run: dry_run
         )
 
         response = GitalyClient.call(