Prevent copying of ContextMenuAllowedScope.

Now that crbug.com/798708 is fixed, ContextMenuAllowedScope can be in a
base::Optional. We delete the copy and assign constructors to prevent
the accidental copying of a ContextMenuAllowedScope into an Optional
instead of the construction being done in place.

Bug: None
Change-Id: Ife88ea31a5aaf31f0c8c55ceb4bc7ca816eef98a
Reviewed-on: https://chromium-review.googlesource.com/850936Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Kevin McNee <mcnee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527044}

third_party/WebKit/Source/core/input/ContextMenuAllowedScope.cpp

@@ -13,6 +13,7 @@ ContextMenuAllowedScope::ContextMenuAllowedScope() {
 }
 
 ContextMenuAllowedScope::~ContextMenuAllowedScope() {
+  DCHECK_GT(g_context_menu_allowed_count, 0U);
   g_context_menu_allowed_count--;
 }
 

third_party/WebKit/Source/core/input/ContextMenuAllowedScope.h

@@ -5,6 +5,7 @@
 #ifndef ContextMenuAllowedScope_h
 #define ContextMenuAllowedScope_h
 
+#include "base/macros.h"
 #include "core/CoreExport.h"
 #include "platform/wtf/Allocator.h"
 
@@ -12,6 +13,7 @@ namespace blink {
 
 class CORE_EXPORT ContextMenuAllowedScope {
   STACK_ALLOCATED();
+  DISALLOW_COPY_AND_ASSIGN(ContextMenuAllowedScope);
 
  public:
   ContextMenuAllowedScope();