Add a getter for the last entered context or microtask context

This is used for internal security checks in eval(). Expose this to
enable the embedder to implement similar security checks.

R=yangguo@chromium.org
BUG=

Change-Id: I10819713b19527622de5ffffac313d126a887c05
Reviewed-on: https://chromium-review.googlesource.com/446106Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43405}

include/v8.h

@@ -6808,6 +6808,14 @@ class V8_EXPORT Isolate {
   /** Returns the last context entered through V8's C++ API. */
   Local<Context> GetEnteredContext();
 
+  /**
+   * Returns either the last context entered through V8's C++ API, or the
+   * context of the currently running microtask while processing microtasks.
+   * If a context is entered while executing a microtask, that context is
+   * returned.
+   */
+  Local<Context> GetEnteredOrMicrotaskContext();
+
   /**
    * Schedules an exception to be thrown when returning to JavaScript.  When an
    * exception has been scheduled it is illegal to invoke any JavaScript

src/api.cc

@@ -8030,6 +8030,18 @@ v8::Local<v8::Context> Isolate::GetEnteredContext() {
   return Utils::ToLocal(i::Handle<i::Context>::cast(last));
 }
 
+v8::Local<v8::Context> Isolate::GetEnteredOrMicrotaskContext() {
+  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
+  i::Handle<i::Object> last;
+  if (isolate->handle_scope_implementer()
+          ->MicrotaskContextIsLastEnteredContext()) {
+    last = isolate->handle_scope_implementer()->MicrotaskContext();
+  } else {
+    last = isolate->handle_scope_implementer()->LastEnteredContext();
+  }
+  if (last.is_null()) return Local<Context>();
+  return Utils::ToLocal(i::Handle<i::Context>::cast(last));
+}
 
 v8::Local<Value> Isolate::ThrowException(v8::Local<v8::Value> value) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);