Remove some bits from document

Attempting to reduce the memory regression seen in crbug.com/1146309.
This doesn't seem like it could possibly account for that entire
regression, but perhaps the story there has many iframes or
something?

Bug: 1146309
Change-Id: I98470080f4398abd4c79d51a0bd24283c85bd3b0
Cq-Do-Not-Cancel-Tryjobs: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2523062
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Auto-Submit: Mason Freed <masonfreed@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825240}

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

@@ -1662,7 +1662,11 @@ class CORE_EXPORT Document : public ContainerNode,
   void MarkFirstPaint();
   void MaybeExecuteDelayedAsyncScripts();
 
-  enum class DeclarativeShadowDomAllowState { kNotSet, kAllow, kDeny };
+  enum class DeclarativeShadowDomAllowState : uint8_t {
+    kNotSet,
+    kAllow,
+    kDeny
+  };
   DeclarativeShadowDomAllowState GetDeclarativeShadowDomAllowState() const;
   void setAllowDeclarativeShadowDom(bool val);
   bool allowDeclarativeShadowDom() const;