Passes file type down to ContentViewer

Instead of ContentViewer attempts to compute file type and render
appropriate viewer type, compute it on the parent RepoEditor having all
file-related information at its disposal and pass it down to
ContentViewer as a prop

app/assets/javascripts/ide/components/repo_editor.vue

 <script>
 import { mapState, mapGetters, mapActions } from 'vuex';
+import { viewerInformationForPath } from '~/vue_shared/components/content_viewer/lib/viewer_utils';
 import flash from '~/flash';
 import ContentViewer from '~/vue_shared/components/content_viewer/content_viewer.vue';
 import DiffViewer from '~/vue_shared/components/diff_viewer/diff_viewer.vue';
@@ -56,6 +57,10 @@ export default {
         active: this.file.viewMode === 'preview',
       };
     },
+    fileType() {
+      const info = viewerInformationForPath(this.file.path);
+      return (info && info.id) || '';
+    },
   },
   watch: {
     file(newVal, oldVal) {
@@ -258,6 +263,7 @@ export default {
       :path="file.rawPath || file.path"
       :file-size="file.size"
       :project-path="file.projectId"
+      :type="fileType"
     />
     <diff-viewer
       v-if="showDiffViewer"

app/assets/javascripts/vue_shared/components/content_viewer/content_viewer.vue

 <script>
-import { viewerInformationForPath } from './lib/viewer_utils';
 import MarkdownViewer from './viewers/markdown_viewer.vue';
 import ImageViewer from './viewers/image_viewer.vue';
 import DownloadViewer from './viewers/download_viewer.vue';
@@ -24,15 +23,18 @@ export default {
       required: false,
       default: '',
     },
+    type: {
+      type: String,
+      required: false,
+      default: '',
+    },
   },
   computed: {
     viewer() {
       if (!this.path) return null;
+      if (!this.type) return DownloadViewer;
 
-      const previewInfo = viewerInformationForPath(this.path);
-      if (!previewInfo) return DownloadViewer;
-
-      switch (previewInfo.id) {
+      switch (this.type) {
         case 'markdown':
           return MarkdownViewer;
         case 'image':

spec/javascripts/vue_shared/components/content_viewer/content_viewer_spec.js

@@ -4,6 +4,7 @@ import axios from '~/lib/utils/axios_utils';
 import contentViewer from '~/vue_shared/components/content_viewer/content_viewer.vue';
 import mountComponent from 'spec/helpers/vue_mount_component_helper';
 import { GREEN_BOX_IMAGE_URL } from 'spec/test_constants';
+import '~/behaviors/markdown/render_gfm';
 
 describe('ContentViewer', () => {
   let vm;
@@ -29,6 +30,7 @@ describe('ContentViewer', () => {
       path: 'test.md',
       content: '*  Test',
       projectPath: 'testproject',
+      type: 'markdown',
     });
 
     const previewContainer = vm.$el.querySelector('.md-previewer');
@@ -44,6 +46,7 @@ describe('ContentViewer', () => {
     createComponent({
       path: GREEN_BOX_IMAGE_URL,
       fileSize: 1024,
+      type: 'image',
     });
 
     setTimeout(() => {