Remove protected section in blink::Deprecation

No one inherits it, so replace protected with private. Also make it
a final class.

Bug: None
Change-Id: Icc7d927c711514f9a64d29290826ae3f824f33bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1616876
Auto-Submit: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Luna Lu <loonybear@chromium.org>
Reviewed-by: Luna Lu <loonybear@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660981}

third_party/blink/renderer/core/frame/deprecation.h

@@ -19,7 +19,7 @@ enum class FeaturePolicyFeature;
 class DocumentLoader;
 class LocalFrame;
 
-class CORE_EXPORT Deprecation {
+class CORE_EXPORT Deprecation final {
   DISALLOW_NEW();
 
  public:
@@ -52,7 +52,7 @@ class CORE_EXPORT Deprecation {
   // Note: this is only public for tests.
   bool IsSuppressed(CSSPropertyID unresolved_property);
 
- protected:
+ private:
   void Suppress(CSSPropertyID unresolved_property);
   void SetReported(WebFeature feature);
   bool GetReported(WebFeature feature) const;