[cpu-profiler] Fix a TSAN false-positive by using std::atomic

TSAN was flakily detecting a race in the Add/RemoveSampler functions.
It could also be fixed by moving the USE(atomic_->Value()); line below
the do loop in the constructor of AtomicGuard.

Given that base::AtomicValue is deprecated and std::atomic has a
compare_exchange operation with std::memory_order_seq_cst, we can just
use std::atomic_bool to fix the TSAN false-positive.

Bug: v8:7702
Change-Id: Id2038ea1ccced7339f45991263e944394e935454
Reviewed-on: https://chromium-review.googlesource.com/c/1288814Reviewed-by: Alexei Filippov <alph@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56794}

src/libsampler/sampler.cc

@@ -12,6 +12,7 @@
 #include <pthread.h>
 #include <signal.h>
 #include <sys/time.h>
+#include <atomic>
 
 #if !V8_OS_QNX && !V8_OS_AIX
 #include <sys/syscall.h>  // NOLINT
@@ -175,16 +176,15 @@ namespace {
 #if defined(USE_SIGNALS)
 typedef std::vector<Sampler*> SamplerList;
 typedef SamplerList::iterator SamplerListIterator;
-typedef base::AtomicValue<bool> AtomicMutex;
+typedef std::atomic_bool AtomicMutex;
 
 class AtomicGuard {
  public:
   explicit AtomicGuard(AtomicMutex* atomic, bool is_blocking = true)
       : atomic_(atomic), is_success_(false) {
     do {
-      // Use Acquire_Load to gain mutual exclusion.
-      USE(atomic_->Value());
-      is_success_ = atomic_->TrySetValue(false, true);
+      bool expected = false;
+      is_success_ = atomic->compare_exchange_weak(expected, true);
     } while (is_blocking && !is_success_);
   }
 
@@ -192,7 +192,7 @@ class AtomicGuard {
 
   ~AtomicGuard() {
     if (!is_success_) return;
-    atomic_->SetValue(false);
+    atomic_->store(false);
   }
 
  private:

test/cctest/cctest.status

@@ -96,9 +96,6 @@
   # BUG(v8:8209). Flaky
   'test-cpu-profiler/Issue1398': [SKIP],
 
-  # BUG(7702). Flaky data race and other test failures.
-  'test-cpu-profiler/MultipleProfilers': [SKIP],
-
   # BUG(7202). The test is flaky.
   'test-cpu-profiler/NativeFrameStackTrace': [SKIP],