[api-minor] Add support for PageMode in the API (issue 8657)

Please refer to https://wwwimages2.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/PDF32000_2008.pdf#page=82.

src/core/obj.js

@@ -313,6 +313,24 @@ var Catalog = (function CatalogClosure() {
       return pageLabels;
     },
 
+    get pageMode() {
+      let obj = this.catDict.get('PageMode');
+      let pageMode = 'UseNone'; // Default value.
+
+      if (isName(obj)) {
+        switch (obj.name) {
+          case 'UseNone':
+          case 'UseOutlines':
+          case 'UseThumbs':
+          case 'FullScreen':
+          case 'UseOC':
+          case 'UseAttachments':
+            pageMode = obj.name;
+        }
+      }
+      return shadow(this, 'pageMode', pageMode);
+    },
+
     get attachments() {
       var xref = this.xref;
       var attachments = null, nameTreeRef;

src/core/worker.js

@@ -770,6 +770,10 @@ var WorkerMessageHandler = {
       }
     );
 
+    handler.on('GetPageMode', function wphSetupGetPageMode(data) {
+      return pdfManager.ensureCatalog('pageMode');
+    });
+
     handler.on('GetAttachments',
       function wphSetupGetAttachments(data) {
         return pdfManager.ensureCatalog('attachments');

src/display/api.js

@@ -568,6 +568,13 @@ var PDFDocumentProxy = (function PDFDocumentProxyClosure() {
     getPageLabels: function PDFDocumentProxy_getPageLabels() {
       return this.transport.getPageLabels();
     },
+    /**
+     * @return {Promise} A promise that is resolved with a {string} containing
+     *   the PageMode name.
+     */
+    getPageMode() {
+      return this.transport.getPageMode();
+    },
     /**
      * @return {Promise} A promise that is resolved with a lookup table for
      * mapping named attachments to their content.
@@ -1939,6 +1946,10 @@ var WorkerTransport = (function WorkerTransportClosure() {
       return this.messageHandler.sendWithPromise('GetPageLabels', null);
     },
 
+    getPageMode() {
+      return this.messageHandler.sendWithPromise('GetPageMode', null);
+    },
+
     getAttachments: function WorkerTransport_getAttachments() {
       return this.messageHandler.sendWithPromise('GetAttachments', null);
     },