Print preview page selection should not require a rerendering of draft pages.

chrome/browser/resources/print_preview/print_preview.js

Index: chrome/browser/resources/print_preview/print_preview.js
diff --git a/chrome/browser/resources/print_preview/print_preview.js b/chrome/browser/resources/print_preview/print_preview.js
index 35ec000338f2f92da3c38462ea19c040f2c210a9..faf553a53f9b4a72940ca1554157e9d8ea23b8d5 100644
--- a/chrome/browser/resources/print_preview/print_preview.js
+++ b/chrome/browser/resources/print_preview/print_preview.js
@@ -23,6 +23,7 @@ const MANAGE_LOCAL_PRINTERS = 'manageLocalPrinters';
 const MORE_PRINTERS = 'morePrinters';
 const SIGN_IN = 'signIn';
 const PRINT_TO_PDF = 'Print to PDF';
+const COMPLETE_PREVIEW_DATA_INDEX = -1;
 
 // State of the print preview settings.
 var printSettings = new PrintSettings();
@@ -62,6 +63,11 @@ var showingSystemDialog = false;
 var firstCloudPrintOptionPos = 0;
 var lastCloudPrintOptionPos = firstCloudPrintOptionPos;
 
+// Store the current previewUid.
+var currentPreviewUid = '';
+
+// True if we need to generate draft preview data.
+var generateDraftData = true;
 
 // TODO(abodenha@chromium.org) A lot of cloud print specific logic has
 // made its way into this file.  Refactor to create a cleaner boundary
@@ -311,7 +317,8 @@ function getSettings() {
        'landscape': layoutSettings.isLandscape(),
        'color': colorSettings.isColor(),
        'printToPDF': printToPDF,
-       'requestID': 0};
+       'requestID': 0,
+       'generateDraftData': generateDraftData};
 
   var printerList = $('printer-list');
   var selectedPrinter = printerList.selectedIndex;
@@ -421,15 +428,42 @@ function sendPrintDocumentRequest() {
 }
 
 /**
+ * Loads the selected preview pages.
+ */
+function loadSelectedPages() {
+  hasPendingPreviewRequest = false;
+  pageSettings.updatePageSelection();
+  var pageSet = pageSettings.previouslySelectedPages;
+  var pageCount = pageSet.length;
+  if (pageCount == 0 || currentPreviewUid == '')
+    return;
+
+  for (var i = 0; i < pageCount; i++)
+    onDidPreviewPage(pageSet[i] - 1, currentPreviewUid);
+  addEventListeners();
+}
+
+/**
  * Asks the browser to generate a preview PDF based on current print settings.
  */
 function requestPrintPreview() {
   hasPendingPreviewRequest = true;
   removeEventListeners();
   printSettings.save();
+  generateDraftData = true;
   if (!isTabHidden)
     showLoadingAnimation();
 
+  if (previewModifiable && hasOnlyPageSettingsChanged()) {
+    loadSelectedPages();
+    generateDraftData = false;
+  } else {
+    pageSettings.updatePageSelection();
+  }
+
+  if (!previewModifiable && pageSettings.totalPageCount > 0)
+    generateDraftData = false;
+
   var settings = getSettings();
   settings.requestID = generatePreviewRequestID();
   chrome.send('getPreview', [JSON.stringify(settings)]);
@@ -829,12 +863,16 @@ function onDidPreviewPage(pageNumber, previewUid) {
   if (!previewModifiable)
     return;
 
-  var pageIndex = pageSettings.previouslySelectedPages.indexOf(pageNumber + 1);
-
   if (checkIfSettingsChangedAndRegeneratePreview())
     return;
+
+  var pageIndex = pageSettings.previouslySelectedPages.indexOf(pageNumber + 1);
+  if (pageIndex == -1)
+    return;
+
+  currentPreviewUid = previewUid;
   if (pageIndex == 0)
-    createPDFPlugin(previewUid);
+    createPDFPlugin(pageNumber);
 
   $('pdf-viewer').loadPreviewPage(
       getPageSrcURL(previewUid, pageNumber), pageIndex);
@@ -864,7 +902,8 @@ function updatePrintPreview(jobTitle,
 
   if (!previewModifiable) {
     // If the preview is not modifiable the plugin has not been created yet.
-    createPDFPlugin(previewUid);
+    currentPreviewUid = previewUid;
+    createPDFPlugin(COMPLETE_PREVIEW_DATA_INDEX);
   }
 
   cr.dispatchSimpleEvent(document, 'updateSummary');
@@ -898,28 +937,41 @@ function checkIfSettingsChangedAndRegeneratePreview() {
 }
 
 /**
+ * Check if only page selection has been changed since the last preview request
+ * and is valid.
+ * @return {boolean} true if the new page selection is valid.
+ */
+function hasOnlyPageSettingsChanged() {
+  var tempPrintSettings = new PrintSettings();
+  tempPrintSettings.save();
+
+  return !!(printSettings.deviceName == tempPrintSettings.deviceName &&
+            printSettings.isLandscape == tempPrintSettings.isLandscape &&
+            pageSettings.hasPageSelectionChangedAndIsValid());
+}
+
+/**
  * Create the PDF plugin or reload the existing one.
- * @param {string} previewUid Preview unique identifier.
+ * @param {number} srcDataIndex Preview data source index.
  */
-function createPDFPlugin(previewUid) {
+function createPDFPlugin(srcDataIndex) {
   var pdfViewer = $('pdf-viewer');
+  var srcURL = getPageSrcURL(currentPreviewUid, srcDataIndex);
   if (pdfViewer) {
     // Need to call this before the reload(), where the plugin resets its
     // internal page count.
     pdfViewer.goToPage('0');
+    pdfViewer.resetPrintPreviewUrl(srcURL);
     pdfViewer.reload();
     pdfViewer.grayscale(!colorSettings.isColor());
     return;
   }
 
-  // Get the complete preview document.
-  var dataIndex = previewModifiable ? '0' : '-1';
-
   pdfViewer = document.createElement('embed');
   pdfViewer.setAttribute('id', 'pdf-viewer');
   pdfViewer.setAttribute('type',
                          'application/x-google-chrome-print-preview-pdf');
-  pdfViewer.setAttribute('src', getPageSrcURL(previewUid, dataIndex));
+  pdfViewer.setAttribute('src', srcURL);
   pdfViewer.setAttribute('aria-live', 'polite');
   pdfViewer.setAttribute('aria-atomic', 'true');
   $('mainview').appendChild(pdfViewer);
@@ -937,7 +989,8 @@ function checkCompatiblePluginExists() {
             dummyPlugin.goToPage &&
             dummyPlugin.removePrintButton &&
             dummyPlugin.loadPreviewPage &&
-            dummyPlugin.printPreviewPageCount);
+            dummyPlugin.printPreviewPageCount &&
+            dummyPlugin.resetPrintPreviewUrl);
 }
 
 window.addEventListener('DOMContentLoaded', onLoad);