[cleanup] Unify the LocalIsolate/Isolate calls on js-heap-broker

We have several ways of doing the Isolate or LocalIsolate calls. Let's
unify it to have one consistent way of doing it.

Bug: v8:7790
Change-Id: I7d860e918406b07e3b8ab2d46e775a2beb5a4397
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2718609Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73048}

src/compiler/js-heap-broker.cc

@@ -3271,11 +3271,11 @@ base::Optional<uint16_t> StringRef::GetFirstChar() {
       return base::nullopt;
     }
 
-    if (broker()->local_isolate()) {
+    if (!broker()->IsMainThread()) {
       return object()->Get(0, broker()->local_isolate());
     } else {
-      // TODO(solanes, v8:7790): Remove this case once we always have a local
-      // isolate, i.e. the inlining phase is done concurrently all the time.
+      // TODO(solanes, v8:7790): Remove this case once the inlining phase is
+      // done concurrently all the time.
       return object()->Get(0);
     }
   }
@@ -3584,9 +3584,8 @@ BIMODAL_ACCESSOR_C(SharedFunctionInfo, int, builtin_id)
 BytecodeArrayRef SharedFunctionInfoRef::GetBytecodeArray() const {
   if (data_->should_access_heap() || FLAG_turbo_direct_heap_access) {
     BytecodeArray bytecode_array;
-    LocalIsolate* local_isolate = broker()->local_isolate();
-    if (local_isolate && !local_isolate->is_main_thread()) {
-      bytecode_array = object()->GetBytecodeArray(local_isolate);
+    if (!broker()->IsMainThread()) {
+      bytecode_array = object()->GetBytecodeArray(broker()->local_isolate());
     } else {
       bytecode_array = object()->GetBytecodeArray(broker()->isolate());
     }
@@ -3603,8 +3602,8 @@ BROKER_SFI_FIELDS(DEF_SFI_ACCESSOR)
 SharedFunctionInfo::Inlineability SharedFunctionInfoRef::GetInlineability()
     const {
   if (data_->should_access_heap()) {
-    if (LocalIsolate* local_isolate = broker()->local_isolate()) {
-      return object()->GetInlineability(local_isolate);
+    if (!broker()->IsMainThread()) {
+      return object()->GetInlineability(broker()->local_isolate());
     } else {
       return object()->GetInlineability(broker()->isolate());
     }

src/compiler/js-heap-broker.h

@@ -251,6 +251,10 @@ class V8_EXPORT_PRIVATE JSHeapBroker {
   bool IsSerializedForCompilation(const SharedFunctionInfoRef& shared,
                                   const FeedbackVectorRef& feedback) const;
 
+  bool IsMainThread() const {
+    return local_isolate() == nullptr || local_isolate()->is_main_thread();
+  }
+
   LocalIsolate* local_isolate() const { return local_isolate_; }
 
   // Return the corresponding canonical persistent handle for {object}. Create
@@ -315,10 +319,6 @@ class V8_EXPORT_PRIVATE JSHeapBroker {
   friend class ObjectData;
   friend class PropertyCellData;
 
-  bool IsMainThread() const {
-    return local_isolate() == nullptr || local_isolate()->is_main_thread();
-  }
-
   // If this returns false, the object is guaranteed to be fully initialized and
   // thus safe to read from a memory safety perspective. The converse does not
   // necessarily hold.