Reland of "Release streamed script resources after it was compiled"

Original issue's description:
> Release streamed script resources after it was compiled
>
> Otherwise, we'd hold on to the resources until the embedder frees them
> which might take a long time
>
> R=marja@chromium.org,verwaest@chromium.org
> BUG=
>
> Committed: https://crrev.com/877dac34465c018bb534b7781fbe242ae4e33c32
> Cr-Commit-Position: refs/heads/master@{#38999}

TBR=marja@chromium.org,verwaest@chromium.org
BUG=chromium:642347

Review-Url: https://codereview.chromium.org/2296733002
Cr-Commit-Position: refs/heads/master@{#39018}

src/api.cc

@@ -2194,9 +2194,10 @@ MaybeLocal<Script> ScriptCompiler::Compile(Local<Context> context,
   }
   has_pending_exception = result.is_null();
   if (has_pending_exception) isolate->ReportPendingMessages();
-  RETURN_ON_FAILED_EXECUTION(Script);
 
-  source->info->clear_script();  // because script goes out of scope.
+  source->Release();
+
+  RETURN_ON_FAILED_EXECUTION(Script);
 
   Local<UnboundScript> generic = ToApiHandle<UnboundScript>(result);
   if (generic.IsEmpty()) return Local<Script>();

src/background-parsing-task.h

@@ -26,6 +26,12 @@ struct StreamedSource {
                  ScriptCompiler::StreamedSource::Encoding encoding)
       : source_stream(source_stream), encoding(encoding) {}
 
+  void Release() {
+    parser.reset();
+    info.reset();
+    zone.reset();
+  }
+
   // Internal implementation of v8::ScriptCompiler::StreamedSource.
   std::unique_ptr<ScriptCompiler::ExternalSourceStream> source_stream;
   ScriptCompiler::StreamedSource::Encoding encoding;