[gn] Enable stricter build flags

src/runtime/runtime-liveedit.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/debug/debug.h"
 #include "src/debug/debug-frames.h"
 #include "src/debug/liveedit.h"
@@ skipping 14 matching lines @@
   CONVERT_ARG_CHECKED(JSValue, script_value, 0);
 
   CHECK(script_value->value()->IsScript());
   Handle<Script> script = Handle<Script>(Script::cast(script_value->value()));
 
   List<Handle<SharedFunctionInfo> > found;
   Heap* heap = isolate->heap();
   {
     HeapIterator iterator(heap);
     HeapObject* heap_obj;
-    while ((heap_obj = iterator.next())) {
+    while ((heap_obj = iterator.next()) != nullptr) {
       if (!heap_obj->IsSharedFunctionInfo()) continue;
       SharedFunctionInfo* shared = SharedFunctionInfo::cast(heap_obj);
       if (shared->script() != *script) continue;
       found.Add(Handle<SharedFunctionInfo>(shared));
     }
   }
 
   Handle<FixedArray> result = isolate->factory()->NewFixedArray(found.length());
   for (int i = 0; i < found.length(); ++i) {
     Handle<SharedFunctionInfo> shared = found[i];
@@ skipping 250 matching lines @@
   // We don't really care what the inlined frame index is, since we are
   // throwing away the entire frame anyways.
   const char* error_message = LiveEdit::RestartFrame(it.javascript_frame());
   if (error_message) {
     return *(isolate->factory()->InternalizeUtf8String(error_message));
   }
   return heap->true_value();
 }
 }  // namespace internal
 }  // namespace v8