Handle null parser in inline code caching

Add a null check for document.GetScriptableDocumentParser() when getting
an inline cache handler.

Bug: chromium:841651
Change-Id: Ie34c23a49c5725766ddf75e5667eb1b2dc7c0baf
Reviewed-on: https://chromium-review.googlesource.com/1052698
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558100}

third_party/blink/renderer/core/script/classic_pending_script.cc

@@ -239,8 +239,13 @@ static SingleCachedMetadataHandler* GetInlineCacheHandler(const String& source,
   if (!RuntimeEnabledFeatures::CacheInlineScriptCodeEnabled())
     return nullptr;
 
+  ScriptableDocumentParser* scriptable_parser =
+      document.GetScriptableDocumentParser();
+  if (!scriptable_parser)
+    return nullptr;
+
   SourceKeyedCachedMetadataHandler* document_cache_handler =
-      document.GetScriptableDocumentParser()->GetInlineScriptCacheHandler();
+      scriptable_parser->GetInlineScriptCacheHandler();
 
   if (!document_cache_handler)
     return nullptr;