Make the DatabaseTracker thread-safe.

WebCore/storage/OriginQuotaManager.cpp

Index: WebCore/storage/OriginQuotaManager.cpp
===================================================================
--- WebCore/storage/OriginQuotaManager.cpp	(revision 55036)
+++ WebCore/storage/OriginQuotaManager.cpp	(working copy)
@@ -42,6 +42,18 @@
 {
 }
 
+bool OriginQuotaManager::tryLock()
+{
+    bool locked = m_usageRecordGuard.tryLock();
+#ifndef NDEBUG
+    if (locked)
+        m_usageRecordGuardLocked = true;
+    else
+        ASSERT(m_usageRecordGuardLocked);
+#endif
+    return locked;
+}
+
 void OriginQuotaManager::lock()
 {
     m_usageRecordGuard.lock();