Worklet: Lazily create PaintWorkletGlobalScopes

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

Index: third_party/WebKit/Source/core/workers/MainThreadWorklet.cpp
diff --git a/third_party/WebKit/Source/core/workers/MainThreadWorklet.cpp b/third_party/WebKit/Source/core/workers/MainThreadWorklet.cpp
index 43ac12846daf9ddca9a6050301035f5223636844..cdec996017a1b9aa6719e9760e4f224861e8a174 100644
--- a/third_party/WebKit/Source/core/workers/MainThreadWorklet.cpp
+++ b/third_party/WebKit/Source/core/workers/MainThreadWorklet.cpp
@@ -33,6 +33,13 @@ WebURLRequest::FetchCredentialsMode ParseCredentialsOption(
 
 MainThreadWorklet::MainThreadWorklet(LocalFrame* frame) : Worklet(frame) {}
 
+WorkletGlobalScopeProxy* MainThreadWorklet::FindAvailableGlobalScope() const {
+  DCHECK(IsMainThread());
+  // TODO(nhiroki): Support the case where there are multiple global scopes.
+  DCHECK_EQ(1u, GetNumberOfGlobalScopes());
+  return proxies_.begin()->get();
+}
+
 // Implementation of the second half of the "addModule(moduleURL, options)"
 // algorithm:
 // https://drafts.css-houdini.org/worklets/#dom-worklet-addmodule
@@ -67,15 +74,14 @@ void MainThreadWorklet::FetchAndInvokeScript(const KURL& module_url_record,
   //   10.2: "Add the WorkletGlobalScope to worklet's WorkletGlobalScopes."
   // "Depending on the type of worklet the user agent may create additional
   // WorkletGlobalScopes at this time."
-  // TODO(nhiroki): Create WorkletGlobalScopes at this point.
+  while (NeedsToCreateGlobalScope())
+    proxies_.insert(CreateGlobalScope());
+  DCHECK_EQ(1u, GetNumberOfGlobalScopes());
 
   // Step 11: "Let pendingTaskStruct be a new pending tasks struct with counter
   // initialized to the length of worklet's WorkletGlobalScopes."
-  // TODO(nhiroki): Introduce the concept of "worklet's WorkletGlobalScopes" and
-  // use the length of it here.
-  constexpr int number_of_global_scopes = 1;
   WorkletPendingTasks* pending_tasks =
-      new WorkletPendingTasks(number_of_global_scopes, resolver);
+      new WorkletPendingTasks(GetNumberOfGlobalScopes(), resolver);
 
   // Step 12: "For each workletGlobalScope in the worklet's
   // WorkletGlobalScopes, queue a task on the workletGlobalScope to fetch and
@@ -83,13 +89,16 @@ void MainThreadWorklet::FetchAndInvokeScript(const KURL& module_url_record,
   // moduleResponsesMap, credentialOptions, outsideSettings, pendingTaskStruct,
   // and promise."
   // TODO(nhiroki): Queue a task instead of executing this here.
-  GetWorkletGlobalScopeProxy()->FetchAndInvokeScript(
-      module_url_record, credentials_mode, pending_tasks);
+  for (const auto& proxy : proxies_) {
+    proxy->FetchAndInvokeScript(module_url_record, credentials_mode,
+                                pending_tasks);
+  }
 }
 
 void MainThreadWorklet::ContextDestroyed(ExecutionContext* execution_context) {
   DCHECK(IsMainThread());
-  GetWorkletGlobalScopeProxy()->TerminateWorkletGlobalScope();
+  for (const auto& proxy : proxies_)
+    proxy->TerminateWorkletGlobalScope();
 }
 
 DEFINE_TRACE(MainThreadWorklet) {