[api] Implement flags for V8 performance ablation study

This Cl adds the two following flags to artificially slow down script
execution in a controlled way:

--script_run_delay      delays the first every v8::Execute per isolate
--script_run_delay_once delays every v8::Execute

Bug: chromium:1193459
Change-Id: I78fcf940513e9f82fde57ff222e95df9202d00a7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2739641Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73710}

src/api/api.cc

@@ -1924,6 +1924,17 @@ MaybeLocal<Value> Script::Run(Local<Context> context) {
   i::TimerEventScope<i::TimerEventExecute> timer_scope(isolate);
   auto fun = i::Handle<i::JSFunction>::cast(Utils::OpenHandle(this));
 
+  // TODO(crbug.com/1193459): remove once ablation study is completed
+  if (i::FLAG_script_run_delay) {
+    v8::base::OS::Sleep(
+        v8::base::TimeDelta::FromMilliseconds(i::FLAG_script_run_delay));
+  }
+  if (i::FLAG_script_run_delay_once && !isolate->did_run_script_delay()) {
+    v8::base::OS::Sleep(
+        v8::base::TimeDelta::FromMilliseconds(i::FLAG_script_run_delay_once));
+    isolate->set_did_run_script_delay(true);
+  }
+
   i::Handle<i::Object> receiver = isolate->global_proxy();
   Local<Value> result;
   has_pending_exception = !ToLocal<Value>(

src/execution/isolate.h

@@ -465,7 +465,9 @@ using DebugObjectCache = std::vector<Handle<HeapObject>>;
   V(bool, detailed_source_positions_for_profiling, FLAG_detailed_line_info)   \
   V(int, embedder_wrapper_type_index, -1)                                     \
   V(int, embedder_wrapper_object_index, -1)                                   \
-  V(compiler::NodeObserver*, node_observer, nullptr)
+  V(compiler::NodeObserver*, node_observer, nullptr)                          \
+  /* Used in combination with --script-run-delay-once */                      \
+  V(bool, did_run_script_delay, false)
 
 #define THREAD_LOCAL_TOP_ACCESSOR(type, name)                         \
   inline void set_##name(type v) { thread_local_top()->name##_ = v; } \

src/flags/flag-definitions.h

@@ -819,6 +819,9 @@ DEFINE_BOOL(turbo_collect_feedback_in_generic_lowering, true,
 DEFINE_BOOL(isolate_script_cache_ageing, true,
             "enable ageing of the isolate script cache.")
 
+DEFINE_INT(script_run_delay, 0, "sleep [ms] on every Script::Run")
+DEFINE_INT(script_run_delay_once, 0, "sleep [ms] on the first Script::Run")
+
 // Favor memory over execution speed.
 DEFINE_BOOL(optimize_for_size, false,
             "Enables optimizations which favor memory size over execution "