[ES6 modules] TraceWrapper from ScriptLoader and ModuleTreeLinkerRegistry

Before this CL, TraceWrapperV8References on ModuleScript were relying on
trace from Modulator->ModuleMap. However, this is insufficient, as
inline module scripts would not have an entry on module map.

This CL fixes the issue by introducing wrapper tracing to ScriptLoader
and ModuleTreeLinkerRegistry->ModuleTreeLinker object graphs.

Bug: 594639, 725816, 732270
Change-Id: Id4672f3daee90ae007c1ce0c9ea3608b246b129e
Reviewed-on: https://chromium-review.googlesource.com/547157
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#482212}
29 files changed