[api] Allow escaping `MaybeLocal` handles on `EscapableHandleScope`

This adds a convenience overload for `EscapableHandleScope::Escape()`
which moves `MaybeLocal<T>`s into the outer scope, like a regular
`Local<T>`.

This basically moves the syntactic clutter of having to write
`maybe_local.FromMaybe(Local<Foo>())` instead of just `maybe_local`
to a central location.

Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I1d87d75c6564b10e8ec34957bdd3eac46ffea917
Reviewed-on: https://chromium-review.googlesource.com/1056529Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53415}

include/v8.h

@@ -1022,6 +1022,11 @@ class V8_EXPORT EscapableHandleScope : public HandleScope {
     return Local<T>(reinterpret_cast<T*>(slot));
   }
 
+  template <class T>
+  V8_INLINE MaybeLocal<T> EscapeMaybe(MaybeLocal<T> value) {
+    return Escape(value.FromMaybe(Local<T>()));
+  }
+
   EscapableHandleScope(const EscapableHandleScope&) = delete;
   void operator=(const EscapableHandleScope&) = delete;
 

test/cctest/test-api.cc

@@ -23889,8 +23889,7 @@ THREADED_TEST(FunctionNew) {
   CHECK(v8::Integer::New(isolate, 17)->Equals(env.local(), result2).FromJust());
 }
 
-
-TEST(EscapeableHandleScope) {
+TEST(EscapableHandleScope) {
   HandleScope outer_scope(CcTest::isolate());
   LocalContext context;
   const int runs = 10;
@@ -23899,7 +23898,12 @@ TEST(EscapeableHandleScope) {
     v8::EscapableHandleScope inner_scope(CcTest::isolate());
     Local<String> value;
     if (i != 0) value = v8_str("escape value");
-    values[i] = inner_scope.Escape(value);
+    if (i < runs / 2) {
+      values[i] = inner_scope.Escape(value);
+    } else {
+      values[i] = inner_scope.EscapeMaybe(v8::MaybeLocal<String>(value))
+                      .ToLocalChecked();
+    }
   }
   for (int i = 0; i < runs; i++) {
     Local<String> expected;