Add a feature spec for protected branch creation.

1. Doesn't seem like there's an easy way to do this for the actual
   branch protection, since we'd have to test an actual `git push`.

2. Testing branch creation the web UI is also not straightforward,
   since the factory repo doesn't have any hooks, and so access checks
   at the `gitlab-shell` level aren't run.

spec/features/protected_branches_spec.rb

+require 'spec_helper'
+
+feature 'Projected Branches', feature: true, js: true do
+  let(:user) { create(:user, :admin) }
+  let(:project) { create(:project) }
+
+  before { login_as(user) }
+
+  def set_protected_branch_name(branch_name)
+    page.execute_script("$('#protected_branch_name').val('#{branch_name}')")
+  end
+
+  describe "explicit protected branches" do
+    it "allows creating explicit protected branches" do
+      visit namespace_project_protected_branches_path(project.namespace, project)
+      set_protected_branch_name('some-branch')
+      click_on "Protect"
+
+      within(".protected-branches-list") { expect(page).to have_content('some-branch') }
+      expect(ProtectedBranch.count).to eq(1)
+      expect(ProtectedBranch.last.name).to eq('some-branch')
+    end
+
+    it "displays the last commit on the matching branch if it exists" do
+      commit = create(:commit, project: project)
+      project.repository.add_branch(user, 'some-branch', commit.id)
+
+      visit namespace_project_protected_branches_path(project.namespace, project)
+      set_protected_branch_name('some-branch')
+      click_on "Protect"
+
+      within(".protected-branches-list") { expect(page).to have_content(commit.id[0..7]) }
+    end
+
+    it "displays an error message if the named branch does not exist" do
+      visit namespace_project_protected_branches_path(project.namespace, project)
+      set_protected_branch_name('some-branch')
+      click_on "Protect"
+
+      within(".protected-branches-list") { expect(page).to have_content('branch was removed') }
+    end
+  end
+
+  describe "wildcard protected branches" do
+    it "allows creating protected branches with a wildcard" do
+      visit namespace_project_protected_branches_path(project.namespace, project)
+      set_protected_branch_name('*-stable')
+      click_on "Protect"
+
+      within(".protected-branches-list") { expect(page).to have_content('*-stable') }
+      expect(ProtectedBranch.count).to eq(1)
+      expect(ProtectedBranch.last.name).to eq('*-stable')
+    end
+
+    it "displays the number of matching branches" do
+      project.repository.add_branch(user, 'production-stable', 'master')
+      project.repository.add_branch(user, 'staging-stable', 'master')
+
+      visit namespace_project_protected_branches_path(project.namespace, project)
+      set_protected_branch_name('*-stable')
+      click_on "Protect"
+
+      within(".protected-branches-list") { expect(page).to have_content("2 matching branches") }
+    end
+
+    it "displays all the branches matching the wildcard" do
+      project.repository.add_branch(user, 'production-stable', 'master')
+      project.repository.add_branch(user, 'staging-stable', 'master')
+      project.repository.add_branch(user, 'development', 'master')
+      create(:protected_branch, project: project, name: "*-stable")
+
+      visit namespace_project_protected_branches_path(project.namespace, project)
+      click_on "2 matching branches"
+
+      within(".protected-branches-list") do
+        expect(page).to have_content("production-stable")
+        expect(page).to have_content("staging-stable")
+        expect(page).not_to have_content("development")
+      end
+    end
+  end
+end