<http://webkit.org/b/68809> IconDatabase::syncThreadMainLoop can assert if wakeSyncTh...

<webkit.org/b/68809> IconDatabase::syncThreadMainLoop can assert if wakeSyncThread is called before thread starts executing

If wakeSyncThread is called before syncThreadMainLoop starts executing then m_syncThreadHasWorkToDo would be set
while executing the body of the sync thread loop, causing us to skip blocking on the condition variable. This would
lead to us hitting the assertion failure due to m_disabledSuddenTerminationForSyncThread being false, unless the main
thread happened to call wakeSyncThread a second time while the first loop iteration was executing.

Reviewed by Anders Carlsson.

* loader/icon/IconDatabase.cpp:
(WebCore::IconDatabase::syncThreadMainLoop): Clear m_syncThreadHasWorkToDo to indicate that we're about to perform
all pending work.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@95961 268f45cc-cd09-0410-ab3c-d52691b4dbfc