LibJS+LibWeb: Log JavaScript exceptions raised by web content

Instead of hiding JS exceptions raised on the web, we now print them to
the debug log. This will make it a bit easier to work out why some web
pages aren't working right. :^)

Libraries/LibJS/Runtime/VM.cpp

@@ -264,8 +264,7 @@ Value VM::construct(Function& function, Function& new_target, Optional<MarkedVal
 
 void VM::throw_exception(Exception* exception)
 {
-#ifdef VM_DEBUG
-    if (exception->value().is_object() && exception->value().as_object().is_error()) {
+    if (should_log_exceptions() && exception->value().is_object() && exception->value().as_object().is_error()) {
         auto& error = static_cast<Error&>(exception->value().as_object());
         dbgln("Throwing JavaScript Error: {}, {}", error.name(), error.message());
 
@@ -276,7 +275,7 @@ void VM::throw_exception(Exception* exception)
             dbgln("  {}", function_name);
         }
     }
-#endif
+
     m_exception = exception;
     unwind(ScopeType::Try);
 }

Libraries/LibJS/Runtime/VM.h

@@ -75,6 +75,9 @@ public:
     static NonnullRefPtr<VM> create();
     ~VM();
 
+    bool should_log_exceptions() const { return m_should_log_exceptions; }
+    void set_should_log_exceptions(bool b) { m_should_log_exceptions = b; }
+
     Heap& heap() { return m_heap; }
     const Heap& heap() const { return m_heap; }
 
@@ -275,6 +278,8 @@ private:
 #undef __JS_ENUMERATE
 
     Shape* m_scope_object_shape { nullptr };
+
+    bool m_should_log_exceptions { false };
 };
 
 template<>

Libraries/LibWeb/DOM/Document.cpp

@@ -488,8 +488,10 @@ Color Document::visited_link_color() const
 static JS::VM& main_thread_vm()
 {
     static RefPtr<JS::VM> vm;
-    if (!vm)
+    if (!vm) {
         vm = JS::VM::create();
+        vm->set_should_log_exceptions(true);
+    }
     return *vm;
 }