Enable PDFViewerUpdate feature by default

Bug: 1048812
Change-Id: I28771f02ae2afd793ab92e52d29cd9665bbb7504
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2613948
Auto-Submit: Daniel Hosseinian <dhoss@chromium.org>
Commit-Queue: dpapad <dpapad@chromium.org>
Reviewed-by: dpapad <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840980}

pdf/pdf_features.cc

@@ -23,7 +23,7 @@ const base::Feature kPdfPartialLoading = {"PdfPartialLoading",
                                           base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kPDFViewerUpdate = {"PDFViewerUpdate",
-                                        base::FEATURE_DISABLED_BY_DEFAULT};
+                                        base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kPdfViewerPresentationMode = {
     "PdfViewerPresentationMode", base::FEATURE_DISABLED_BY_DEFAULT};