Allow users to import cross-repository pull requests from GitHub

doc/workflow/importing/import_projects_from_github.md

@@ -18,9 +18,6 @@ At its current state, GitHub importer can import:
 
 With GitLab 8.7+, references to pull requests and issues are preserved.
 
-It is not yet possible to import your cross-repository pull requests (those from
-forks). We are working on improving this in the near future.
-
 The importer page is visible when you [create a new project][new-project].
 Click on the **GitHub** link and, if you are logged in via the GitHub
 integration, you will be redirected to GitHub for permission to access your

lib/gitlab/github_import/pull_request_formatter.rb

@@ -33,7 +33,7 @@ module Gitlab
       end
 
       def valid?
-        source_branch.valid? && target_branch.valid? && !cross_project?
+        source_branch.valid? && target_branch.valid?
       end
 
       def source_branch
@@ -68,10 +68,6 @@ module Gitlab
         raw_data.body || ""
       end
 
-      def cross_project?
-        source_branch_repo.id != target_branch_repo.id
-      end
-
       def description
         formatter.author_line(author) + body
       end

spec/lib/gitlab/github_import/pull_request_formatter_spec.rb

@@ -178,8 +178,8 @@ describe Gitlab::GithubImport::PullRequestFormatter, lib: true do
       let(:source_repo) { double(id: 2) }
       let(:raw_data) { double(base_data) }
 
-      it 'returns false' do
-        expect(pull_request.valid?).to eq false
+      it 'returns true' do
+        expect(pull_request.valid?).to eq true
       end
     end
 
@@ -187,8 +187,8 @@ describe Gitlab::GithubImport::PullRequestFormatter, lib: true do
       let(:target_repo) { double(id: 2) }
       let(:raw_data) { double(base_data) }
 
-      it 'returns false' do
-        expect(pull_request.valid?).to eq false
+      it 'returns true' do
+        expect(pull_request.valid?).to eq true
       end
     end
   end