remove use of {,un}setPendingActivity from DOMFileSystem.

Source/modules/filesystem/DOMFileSystem.cpp

Index: Source/modules/filesystem/DOMFileSystem.cpp
diff --git a/Source/modules/filesystem/DOMFileSystem.cpp b/Source/modules/filesystem/DOMFileSystem.cpp
index dba053248136155e7fffec7686e6d0c85a38b3ef..5acc11eb06a23ccd6b90429637c741fb78ff8dc2 100644
--- a/Source/modules/filesystem/DOMFileSystem.cpp
+++ b/Source/modules/filesystem/DOMFileSystem.cpp
@@ -88,6 +88,7 @@ PassRefPtrWillBeRawPtr<DOMFileSystem> DOMFileSystem::createIsolatedFileSystem(Ex
 DOMFileSystem::DOMFileSystem(ExecutionContext* context, const String& name, FileSystemType type, const KURL& rootURL)
     : DOMFileSystemBase(context, name, type, rootURL)
     , ActiveDOMObject(context)
+    , m_numberOfPendingCallbacks(0)
 {
     ScriptWrappable::init(this);
 }
@@ -99,12 +100,19 @@ PassRefPtrWillBeRawPtr<DirectoryEntry> DOMFileSystem::root()
 
 void DOMFileSystem::addPendingCallbacks()
 {
-    setPendingActivity(this);
+    ++m_numberOfPendingCallbacks;
 }
 
 void DOMFileSystem::removePendingCallbacks()
 {
-    unsetPendingActivity(this);
+    ASSERT(m_numberOfPendingCallbacks > 0);
+    --m_numberOfPendingCallbacks;
+}
+
+bool DOMFileSystem::hasPendingActivity() const
+{
+    ASSERT(m_numberOfPendingCallbacks >= 0);
+    return m_numberOfPendingCallbacks;
 }
 
 void DOMFileSystem::reportError(PassOwnPtr<ErrorCallback> errorCallback, PassRefPtrWillBeRawPtr<FileError> fileError)