Add watchdog timer polling for the DFG.
https://bugs.webkit.org/show_bug.cgi?id=115134.

Reviewed by Geoffrey Garen.

The strategy is to add a speculation check to the DFG generated code to
test if the watchdog timer has fired or not. If the watchdog timer has
fired, the generated code will do an OSR exit to the baseline JIT, and
let it handle servicing the watchdog timer.

If the watchdog is not enabled, this speculation check will not be
emitted.

* API/tests/testapi.c:
(currentCPUTime_callAsFunction):
(extendTerminateCallback):
(main):
- removed try/catch statements so that we can test the watchdog on the DFG.
- added JS bindings to a native currentCPUTime() function so that the timeout
  tests can be more accurate.
- also shortened the time values so that the tests can complete sooner.

* bytecode/ExitKind.h:
* dfg/DFGAbstractState.cpp:
(JSC::DFG::AbstractState::executeEffects):
* dfg/DFGByteCodeParser.cpp:
(JSC::DFG::ByteCodeParser::parseBlock):
* dfg/DFGFixupPhase.cpp:
(JSC::DFG::FixupPhase::fixupNode):
* dfg/DFGNodeType.h:
* dfg/DFGPredictionPropagationPhase.cpp:
(JSC::DFG::PredictionPropagationPhase::propagate):
* dfg/DFGSpeculativeJIT32_64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* dfg/DFGSpeculativeJIT64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* runtime/Watchdog.cpp:
(JSC::Watchdog::setTimeLimit):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149089 268f45cc-cd09-0410-ab3c-d52691b4dbfc