Remove `PDFViewerApplication.setScale` and further simplify the `scalechange` event handler (issue 6158)

This finally fixes 6158.

web/viewer.js

@@ -298,7 +298,7 @@ var PDFViewerApplication = {
       newScale = Math.ceil(newScale * 10) / 10;
       newScale = Math.min(MAX_SCALE, newScale);
     } while (--ticks > 0 && newScale < MAX_SCALE);
-    this.setScale(newScale, true);
+    this.pdfViewer.currentScaleValue = newScale;
   },
 
   zoomOut: function pdfViewZoomOut(ticks) {
@@ -308,7 +308,7 @@ var PDFViewerApplication = {
       newScale = Math.floor(newScale * 10) / 10;
       newScale = Math.max(MIN_SCALE, newScale);
     } while (--ticks > 0 && newScale > MIN_SCALE);
-    this.setScale(newScale, true);
+    this.pdfViewer.currentScaleValue = newScale;
   },
 
   get pagesCount() {
@@ -969,14 +969,14 @@ var PDFViewerApplication = {
     } else if (storedHash) {
       this.pdfLinkService.setHash(storedHash);
     } else if (scale) {
-      this.setScale(scale, true);
+      this.pdfViewer.currentScaleValue = scale;
       this.page = 1;
     }
 
     if (!this.pdfViewer.currentScaleValue) {
       // Scale was not initialized: invalid bookmark or scale was not specified.
       // Setting the default one.
-      this.setScale(DEFAULT_SCALE_VALUE, true);
+      this.pdfViewer.currentScaleValue = DEFAULT_SCALE_VALUE;
     }
   },
 
@@ -1172,10 +1172,6 @@ var PDFViewerApplication = {
     this.forceRendering();
   },
 
-  setScale: function (value, resetAutoSettings) {
-    this.pdfViewer.currentScaleValue = value;
-  },
-
   rotatePages: function pdfViewRotatePages(delta) {
     var pageNumber = this.page;
     this.pageRotation = (this.pageRotation + 360 + delta) % 360;
@@ -1443,10 +1439,9 @@ function webViewerInitialized() {
     }
   });
 
-  document.getElementById('scaleSelect').addEventListener('change',
-    function() {
-      PDFViewerApplication.setScale(this.value, false);
-    });
+  document.getElementById('scaleSelect').addEventListener('change', function() {
+    PDFViewerApplication.pdfViewer.currentScaleValue = this.value;
+  });
 
   document.getElementById('presentationMode').addEventListener('click',
     SecondaryToolbar.presentationModeClick.bind(SecondaryToolbar));
@@ -1748,13 +1743,9 @@ window.addEventListener('scalechange', function scalechange(evt) {
   document.getElementById('zoomOut').disabled = (evt.scale === MIN_SCALE);
   document.getElementById('zoomIn').disabled = (evt.scale === MAX_SCALE);
 
-  if (evt.presetValue) {
-    selectScaleOption(evt.presetValue);
-    updateViewarea();
-    return;
-  }
-
-  var predefinedValueFound = selectScaleOption('' + evt.scale);
+  // Update the 'scaleSelect' DOM element.
+  var predefinedValueFound = selectScaleOption(evt.presetValue ||
+                                               '' + evt.scale);
   if (!predefinedValueFound) {
     var customScaleOption = document.getElementById('customScaleOption');
     var customScale = Math.round(evt.scale * 10000) / 100;
@@ -1889,7 +1880,7 @@ window.addEventListener('keydown', function keydown(evt) {
           // keeping it unhandled (to restore page zoom to 100%)
           setTimeout(function () {
             // ... and resetting the scale after browser adjusts its scale
-            PDFViewerApplication.setScale(DEFAULT_SCALE_VALUE, true);
+            pdfViewer.currentScaleValue = DEFAULT_SCALE_VALUE;
           });
           handled = false;
         }