Merge pull request #6122 from Snuffleupagus/issue-6121

Fix a typo causing a TypeError when attempting to call pdfHistory_clearHistoryState (issue 6121)

web/viewer.js

@@ -796,7 +796,7 @@ var PDFViewerApplication = {
         // The browsing history is only enabled when the viewer is standalone,
         // i.e. not when it is embedded in a web page.
         if (!self.preferenceShowPreviousViewOnLoad) {
-          PDFHistory.clearHistoryState();
+          self.pdfHistory.clearHistoryState();
         }
         self.pdfHistory.initialize(self.documentFingerprint);