Make the DatabaseTracker thread-safe.

WebCore/platform/sql/SQLiteDatabase.h

Index: WebCore/platform/sql/SQLiteDatabase.h
===================================================================
--- WebCore/platform/sql/SQLiteDatabase.h	(revision 55036)
+++ WebCore/platform/sql/SQLiteDatabase.h	(working copy)
@@ -97,7 +97,7 @@
     const char* lastErrorMsg();
     
     sqlite3* sqlite3Handle() const {
-        ASSERT(currentThread() == m_openingThread);
+        ASSERT(m_sharable || currentThread() == m_openingThread);
         return m_db;
     }
     
@@ -108,6 +108,12 @@
     void unlock();
     bool isAutoCommitOn() const;
 
+    // Set this flag to allow access from multiple threads.  Not all multi-threaded accesses are safe!
+    // See http://www.sqlite.org/cvstrac/wiki?p=MultiThreading for more info, and you must be running with compile flags and SQLite version appropriate
+    // to your cross-thread uses.
+    bool sharable() { return m_sharable; }
+    void setSharable(bool sharable) { m_sharable = sharable; }
+
 private:
     static int authorizerFunction(void*, int, const char*, const char*, const char*, const char*);
 
@@ -120,6 +126,7 @@
     int m_pageSize;
     
     bool m_transactionInProgress;
+    bool m_sharable;
     
     Mutex m_authorizerLock;
     RefPtr<DatabaseAuthorizer> m_authorizer;