Improve ScriptForbiddenScope handling in cross-threaded code.

third_party/WebKit/Source/platform/ScriptForbiddenScope.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "platform/ScriptForbiddenScope.h"
 
 #include "wtf/Assertions.h"
 #include "wtf/MainThread.h"
 
 namespace blink {
 
 static unsigned s_scriptForbiddenCount = 0;
 
 ScriptForbiddenScope::ScriptForbiddenScope()
 {
-    ASSERT(isMainThread());
-    ++s_scriptForbiddenCount;
+    enter();
 }
 
 ScriptForbiddenScope::~ScriptForbiddenScope()
 {
-    ASSERT(isMainThread());
-    ASSERT(s_scriptForbiddenCount);
-    --s_scriptForbiddenCount;
+    exit();
 }
 
 void ScriptForbiddenScope::enter()
 {
     ASSERT(isMainThread());
     ++s_scriptForbiddenCount;
 }
 
 void ScriptForbiddenScope::exit()
 {
@@ skipping 11 matching lines @@
 {
     if (isMainThread())
         m_change.emplace(s_scriptForbiddenCount, 0);
 }
 
 ScriptForbiddenScope::AllowUserAgentScript::~AllowUserAgentScript()
 {
     ASSERT(!isMainThread() || !s_scriptForbiddenCount);
 }
 
+ScriptForbiddenIfMainThreadScope::ScriptForbiddenIfMainThreadScope()
+{
+    if (isMainThread())
+        ScriptForbiddenScope::enter();
+}
+
+ScriptForbiddenIfMainThreadScope::~ScriptForbiddenIfMainThreadScope()
+{
+    if (isMainThread())
+        ScriptForbiddenScope::exit();
+}
 } // namespace blink