Remove the kViewSourceDocumentClass (unused) document class

It seems that the kDefaultDocumentClass should work just the same,
as nothing currently checks for kViewSourceDocumentClass.

Bug: 920571
Change-Id: I63088c00c0fa773f8c597f0f88768a984a6fc994
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2424628
Commit-Queue: Joey Arhar <jarhar@chromium.org>
Auto-Submit: Mason Freed <masonfreed@chromium.org>
Reviewed-by: Joey Arhar <jarhar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809519}

third_party/blink/renderer/core/dom/document.h

@@ -242,7 +242,6 @@ enum DocumentClass {
   kMediaDocumentClass = 1 << 4,
   kSVGDocumentClass = 1 << 5,
   kXMLDocumentClass = 1 << 6,
-  kViewSourceDocumentClass = 1 << 7,
 };
 
 enum ShadowCascadeOrder {

third_party/blink/renderer/core/html/html_view_source_document.cc

@@ -43,8 +43,7 @@
 namespace blink {
 
 HTMLViewSourceDocument::HTMLViewSourceDocument(const DocumentInit& initializer)
-    : HTMLDocument(initializer, kViewSourceDocumentClass),
-      type_(initializer.GetMimeType()) {
+    : HTMLDocument(initializer), type_(initializer.GetMimeType()) {
   SetIsViewSource(true);
 
   // FIXME: Why do view-source pages need to load in quirks mode?