Worklet: Lazily create PaintWorkletGlobalScopes

third_party/WebKit/Source/core/workers/MainThreadWorklet.h

Index: third_party/WebKit/Source/core/workers/MainThreadWorklet.h
diff --git a/third_party/WebKit/Source/core/workers/MainThreadWorklet.h b/third_party/WebKit/Source/core/workers/MainThreadWorklet.h
index e6b5c8578b3986d939aa7b2c42146a6d8ced3aa9..8350189cccc1a6b55bf06ba2536692d1f2825101 100644
--- a/third_party/WebKit/Source/core/workers/MainThreadWorklet.h
+++ b/third_party/WebKit/Source/core/workers/MainThreadWorklet.h
@@ -15,6 +15,7 @@ namespace blink {
 
 class LocalFrame;
 class ScriptPromiseResolver;
+class WorkletGlobalScopeProxy;
 
 // A MainThreadWorklet is a worklet that runs only on the main thread.
 // TODO(nhiroki): This is a temporary class to support module loading for main
@@ -38,6 +39,19 @@ class CORE_EXPORT MainThreadWorklet : public Worklet {
  protected:
   explicit MainThreadWorklet(LocalFrame*);
 
+  // Creates WorkletGlobalScope and adds it into |global_scope_proxies_| if
+  // there are not global scopes or additional global scopes are necessary.
+  virtual void AddWorkletGlobalScopesIfNeeded() = 0;

[kouhei (in TOK), 2017/05/08 13:13:19]

Can we have a virtual WorkletGlobalScopeProxy* CreateWorkletGlobalScope() = 0;
instead and have AddWorkletGlobalScopesIfNeeded + global_scope_proxies_
non-virtual?
This is based on assumption that every AddWorkletGlobalScopesIfNeeded will
actually global_scope_proxies_.insert(std::move(proxy)) at the end.

[nhiroki, 2017/05/10 09:01:31]

Replaced this with NeedsToCreateGlobalScope() and CreateGlobalScope().

+
+  // "A Worklet has a list of the worklet's WorkletGlobalScopes. Initially this
+  // list is empty; it is populated when the user agent chooses to create its
+  // WorkletGlobalScope."
+  // https://drafts.css-houdini.org/worklets/#worklet-section
+  // TODO(nhiroki): Make (Paint)WorkletGlobalScopeProxy GC-managed object to
+  // avoid that GC graphs are disjointed (PaintWorkletGlobalScopeProxy has a
+  // persistent holder for PaintWorkletGlobalscope).

[kouhei (in TOK), 2017/05/08 13:13:19]

+1. Can we give a crbug # to this?

[nhiroki, 2017/05/10 09:01:31]

Added a crbug link.

+  WTF::HashSet<std::unique_ptr<WorkletGlobalScopeProxy>> global_scope_proxies_;
+
  private:
   void FetchAndInvokeScript(const KURL& module_url_record,
                             ScriptPromiseResolver*);