Watchdog timer should be lazily allocated
https://bugs.webkit.org/show_bug.cgi?id=133135

Reviewed by Geoffrey Garen.

Source/JavaScriptCore:
We incur a noticeable amount of overhead on some benchmarks due to checking if the Watchdog ever fired.
There is no reason to do this checking if we never activated the Watchdog, which can only be done through
JSContextGroupSetExecutionTimeLimit or JSContextGroupClearExecutionTimeLimit.

By allocating the Watchdog lazily on the VM we can avoid all of the associated overhead when we don't use
these two API functions (which is true of most clients).

* API/JSContextRef.cpp:
(JSContextGroupSetExecutionTimeLimit):
(JSContextGroupClearExecutionTimeLimit):
* dfg/DFGByteCodeParser.cpp:
(JSC::DFG::ByteCodeParser::parseBlock):
* dfg/DFGSpeculativeJIT32_64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* dfg/DFGSpeculativeJIT64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* interpreter/Interpreter.cpp:
(JSC::Interpreter::execute):
(JSC::Interpreter::executeCall):
(JSC::Interpreter::executeConstruct):
* jit/JITOpcodes.cpp:
(JSC::JIT::emit_op_loop_hint):
(JSC::JIT::emitSlow_op_loop_hint):
* jit/JITOperations.cpp:
* llint/LLIntSlowPaths.cpp:
(JSC::LLInt::LLINT_SLOW_PATH_DECL):
* runtime/VM.h:
* runtime/Watchdog.cpp:
(JSC::Watchdog::Scope::Scope): Deleted.
(JSC::Watchdog::Scope::~Scope): Deleted.
* runtime/Watchdog.h:
(JSC::Watchdog::Scope::Scope):
(JSC::Watchdog::Scope::~Scope):

Source/WebCore:
No new tests.

We incur a noticeable amount of overhead on some benchmarks due to checking if the Watchdog ever fired.
There is no reason to do this checking if we never activated the Watchdog, which can only be done through
JSContextGroupSetExecutionTimeLimit or JSContextGroupClearExecutionTimeLimit.

By allocating the Watchdog lazily on the VM we can avoid all of the associated overhead when we don't use
these two API functions (which is true of most clients).

* bindings/js/JSEventListener.cpp:
(WebCore::JSEventListener::handleEvent):
* bindings/js/WorkerScriptController.cpp:
(WebCore::WorkerScriptController::evaluate):
(WebCore::WorkerScriptController::scheduleExecutionTermination):
(WebCore::WorkerScriptController::isExecutionTerminating):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@169139 268f45cc-cd09-0410-ab3c-d52691b4dbfc