Atomic accessor for Isolate::code_coverage_mode

Change Isolate::code_coverage_mode to an atomic such that access from
the background thread is safe.

Bug: v8:11378
Change-Id: I26d6915b1662ba022ea6a173a87d184d3ac7cd3b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2666691
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72530}

src/execution/isolate.h

@@ -455,8 +455,6 @@ using DebugObjectCache = std::vector<Handle<HeapObject>>;
   V(bool, formatting_stack_trace, false)                                      \
   /* Perform side effect checks on function call and API callbacks. */        \
   V(DebugInfo::ExecutionMode, debug_execution_mode, DebugInfo::kBreakpoints)  \
-  /* Current code coverage mode */                                             \
-  V(debug::CoverageMode, code_coverage_mode, debug::CoverageMode::kBestEffort) \
   V(debug::TypeProfileMode, type_profile_mode, debug::TypeProfileMode::kNone) \
   V(bool, disable_bytecode_flushing, false)                                   \
   V(int, last_console_context_id, 0)                                          \
@@ -1586,6 +1584,13 @@ class V8_EXPORT_PRIVATE Isolate final : private HiddenFactory {
 
   RAILMode rail_mode() { return rail_mode_.load(); }
 
+  void set_code_coverage_mode(debug::CoverageMode coverage_mode) {
+    code_coverage_mode_.store(coverage_mode, std::memory_order_relaxed);
+  }
+  debug::CoverageMode code_coverage_mode() const {
+    return code_coverage_mode_.load(std::memory_order_relaxed);
+  }
+
   double LoadStartTimeMs();
 
   void IsolateInForegroundNotification();
@@ -1840,6 +1845,8 @@ class V8_EXPORT_PRIVATE Isolate final : private HiddenFactory {
       host_import_module_dynamically_callback_ = nullptr;
   HostImportModuleDynamicallyWithImportAssertionsCallback
       host_import_module_dynamically_with_import_assertions_callback_ = nullptr;
+  std::atomic<debug::CoverageMode> code_coverage_mode_{
+      debug::CoverageMode::kBestEffort};
 
   // Helper function for RunHostImportModuleDynamicallyCallback.
   // Unpacks import assertions, if present, from the second argument to dynamic