249         tab_descriptor = self._generate_tab_descriptor(tab)
250         self._tabs[tab_descriptor] = tab
252         return tab_descriptor
286     def get_tab_by_descriptor(self, tab_descriptor):  argument
292         return self._tabs[tab_descriptor]
296     def close_tab(self, tab_descriptor):  argument
302         if tab_descriptor not in self._tabs:
303             raise RuntimeError('There is no tab for %s' % tab_descriptor)
304         tab = self._tabs[tab_descriptor]
305         del self._tabs[tab_descriptor]
311             self, tab_descriptor, expression, timeout):  argument
318         if tab_descriptor not in self._tabs:
319             raise RuntimeError('There is no tab for %s' % tab_descriptor)
320         self._tabs[tab_descriptor].WaitForJavaScriptCondition(
324     def execute_javascript(self, tab_descriptor, statement, timeout):  argument
331         if tab_descriptor not in self._tabs:
332             raise RuntimeError('There is no tab for %s' % tab_descriptor)
333         self._tabs[tab_descriptor].ExecuteJavaScript(
337     def evaluate_javascript(self, tab_descriptor, expression, timeout):  argument
345         if tab_descriptor not in self._tabs:
346             raise RuntimeError('There is no tab for %s' % tab_descriptor)
347         return self._tabs[tab_descriptor].EvaluateJavaScript(