[gin] Enter the isolate before deleting a context

Deleting the context writes to the external pointer table and to the
heap, hence we must enter the isolate before deleting the context.

This is blocking a new DCHECK in v8: https://crrev.com/c/6387098

For consistency, we should also move the HandleScope from the
`PerContextData` destructor to the `ShellRunner` destructor, but this
causes failures in other users of `PerContextData`, so this is left for
a follow-up CL.

Drive-by cleanup: Remove `using` declarations which were mostly not
used, and if they were then inconsistently.

R=mlippautz@chromium.org

Bug: 396607238
Change-Id: I110a72c047d3a719e9606fc98f32f2b0536bb656
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6394240
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1438234}

gin/shell_runner.cc

@@ -13,23 +13,16 @@
 #include "gin/try_catch.h"
 #include "v8/include/v8-script.h"
 
-using v8::Context;
-using v8::HandleScope;
-using v8::Isolate;
-using v8::Object;
-using v8::ObjectTemplate;
-using v8::Script;
-
 namespace gin {
 
 ShellRunnerDelegate::ShellRunnerDelegate() = default;
 
 ShellRunnerDelegate::~ShellRunnerDelegate() = default;
 
-v8::Local<ObjectTemplate> ShellRunnerDelegate::GetGlobalTemplate(
+v8::Local<v8::ObjectTemplate> ShellRunnerDelegate::GetGlobalTemplate(
     ShellRunner* runner,
     v8::Isolate* isolate) {
-  return v8::Local<ObjectTemplate>();
+  return v8::Local<v8::ObjectTemplate>();
 }
 
 void ShellRunnerDelegate::DidCreateContext(ShellRunner* runner) {
@@ -46,12 +39,12 @@ void ShellRunnerDelegate::UnhandledException(ShellRunner* runner,
   NOTREACHED() << try_catch.GetStackTrace();
 }
 
-ShellRunner::ShellRunner(ShellRunnerDelegate* delegate, Isolate* isolate)
+ShellRunner::ShellRunner(ShellRunnerDelegate* delegate, v8::Isolate* isolate)
     : delegate_(delegate) {
   v8::Isolate::Scope isolate_scope(isolate);
-  HandleScope handle_scope(isolate);
-  v8::Local<v8::Context> context =
-      Context::New(isolate, NULL, delegate_->GetGlobalTemplate(this, isolate));
+  v8::HandleScope handle_scope(isolate);
+  v8::Local<v8::Context> context = v8::Context::New(
+      isolate, nullptr, delegate_->GetGlobalTemplate(this, isolate));
 
   context_holder_ = std::make_unique<ContextHolder>(isolate);
   context_holder_->SetContext(context);
@@ -61,16 +54,22 @@ ShellRunner::ShellRunner(ShellRunnerDelegate* delegate, Isolate* isolate)
   delegate_->DidCreateContext(this);
 }
 
-ShellRunner::~ShellRunner() = default;
+ShellRunner::~ShellRunner() {
+  // Deleting the ContextRunner deletes the contained PerContextData, which
+  // writes to the V8 heap in its destructor. Hence enter the isolate before
+  // doing that.
+  v8::Isolate::Scope isolate_scope(GetContextHolder()->isolate());
+  context_holder_.reset();
+}
 
 v8::MaybeLocal<v8::Value> ShellRunner::Run(const std::string& source,
                                            const std::string& resource_name) {
   v8::Isolate* isolate = GetContextHolder()->isolate();
   TryCatch try_catch(isolate);
   v8::ScriptOrigin origin(StringToV8(isolate, resource_name));
-  auto maybe_script = Script::Compile(GetContextHolder()->context(),
-                                      StringToV8(isolate, source), &origin);
-  v8::Local<Script> script;
+  auto maybe_script = v8::Script::Compile(GetContextHolder()->context(),
+                                          StringToV8(isolate, source), &origin);
+  v8::Local<v8::Script> script;
   if (!maybe_script.ToLocal(&script)) {
     delegate_->UnhandledException(this, try_catch);
     return v8::MaybeLocal<v8::Value>();
@@ -83,7 +82,7 @@ ContextHolder* ShellRunner::GetContextHolder() {
   return context_holder_.get();
 }
 
-v8::MaybeLocal<v8::Value> ShellRunner::Run(v8::Local<Script> script) {
+v8::MaybeLocal<v8::Value> ShellRunner::Run(v8::Local<v8::Script> script) {
   TryCatch try_catch(GetContextHolder()->isolate());
   delegate_->WillRunScript(this);