Make the DatabaseTracker thread-safe.

WebCore/storage/Database.cpp

Index: WebCore/storage/Database.cpp
===================================================================
--- WebCore/storage/Database.cpp	(revision 55036)
+++ WebCore/storage/Database.cpp	(working copy)
@@ -352,6 +352,10 @@
 
     m_scriptExecutionContext->databaseThread()->scheduleImmediateTask(task.release());
     synchronizer.waitForTaskCompletion();
+
+    // DatabaseCloseTask tells Database::close not to do this, so that we can get it over with here.
+    m_scriptExecutionContext->removeOpenDatabase(this);
+    DatabaseTracker::tracker().removeOpenDatabase(this);
 }
 
 class ContextRemoveOpenDatabaseTask : public ScriptExecutionContext::Task {
@@ -378,7 +382,7 @@
     RefPtr<Database> m_database;
 };
 
-void Database::close()
+void Database::close(bool removeDatabaseFromContext)
 {
     RefPtr<Database> protect = this;
 
@@ -407,7 +411,10 @@
     }
 
     m_scriptExecutionContext->databaseThread()->unscheduleDatabaseTasks(this);
-    m_scriptExecutionContext->postTask(ContextRemoveOpenDatabaseTask::create(this));
+    // In some cases the context initiated this call, so it'll take care of the cleanup by itself, synchronously.  This lets it make sure that the
+    // cleanup completes by a given time.
+    if (removeDatabaseFromContext)
+        m_scriptExecutionContext->postTask(ContextRemoveOpenDatabaseTask::create(this));
 }
 
 void Database::stop()