[generators] Implement %GeneratorGetSourcePosition.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index a5da88a0b3b2e0b5e44b17e0918d17655ea38e09..34532f1081c2f0d5456415e1a2fa249da4d079a5 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -18863,5 +18863,19 @@ void PropertyCell::SetValueWithInvalidation(Handle<PropertyCell> cell,
   }
 }
 
+int JSGeneratorObject::source_position() const {
+  CHECK(is_suspended());
+  if (function()->shared()->HasBytecodeArray()) {
+    // New-style generators.
+    int offset = Smi::cast(input())->value();
+    return function()->shared()->bytecode_array()->SourcePosition(offset);
+  } else {
+    // Old-style generators.
+    int offset = continuation();
+    CHECK(0 <= offset && offset < function()->code()->instruction_size());
+    return function()->code()->SourcePosition(offset);
+  }
+}
+
 }  // namespace internal
 }  // namespace v8