Worklet: Lazily create PaintWorkletGlobalScopes

third_party/WebKit/Source/modules/csspaint/PaintWorklet.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "modules/csspaint/PaintWorklet.h"
 
 #include "bindings/core/v8/V8BindingForCore.h"
 #include "core/dom/Document.h"
 #include "core/frame/LocalFrame.h"
 #include "modules/csspaint/PaintWorkletGlobalScope.h"
 
 namespace blink {
 
 // static
 PaintWorklet* PaintWorklet::Create(LocalFrame* frame) {
   return new PaintWorklet(frame);
 }
 
-PaintWorklet::PaintWorklet(LocalFrame* frame)
-    : MainThreadWorklet(frame),
-      global_scope_proxy_(
-          WTF::MakeUnique<PaintWorkletGlobalScopeProxy>(frame)) {}
+PaintWorklet::PaintWorklet(LocalFrame* frame) : MainThreadWorklet(frame) {}
 
 PaintWorklet::~PaintWorklet() = default;
 
-WorkletGlobalScopeProxy* PaintWorklet::GetWorkletGlobalScopeProxy() const {
-  return global_scope_proxy_.get();
-}
-
 CSSPaintDefinition* PaintWorklet::FindDefinition(const String& name) {
-  return global_scope_proxy_->FindDefinition(name);
+  // TODO(nhiroki): Support the case where there are multiple global scopes.
+  DCHECK_EQ(1u, global_scope_proxies_.size());
+  PaintWorkletGlobalScopeProxy* proxy =
+      PaintWorkletGlobalScopeProxy::From(global_scope_proxies_.begin()->get());
+  return proxy->FindDefinition(name);
 }
 
 void PaintWorklet::AddPendingGenerator(const String& name,
                                        CSSPaintImageGeneratorImpl* generator) {
-  return global_scope_proxy_->AddPendingGenerator(name, generator);
+  // TODO(nhiroki): Support the case where there are multiple global scopes.
+  DCHECK_EQ(1u, global_scope_proxies_.size());
+  PaintWorkletGlobalScopeProxy* proxy =
+      PaintWorkletGlobalScopeProxy::From(global_scope_proxies_.begin()->get());
+  return proxy->AddPendingGenerator(name, generator);
 }
 
 DEFINE_TRACE(PaintWorklet) {
   MainThreadWorklet::Trace(visitor);
 }
 
+void PaintWorklet::AddWorkletGlobalScopesIfNeeded() {
+  // "The user agent must have, and select from at least two
+  // PaintWorkletGlobalScopes in the worklet's WorkletGlobalScopes list, unless
+  // the user agent is under memory constraints."
+  // https://drafts.css-houdini.org/css-paint-api-1/#drawing-an-image
+  // TODO(nhiroki): Create at least two global scopes.
+  if (!global_scope_proxies_.IsEmpty())
+    return;
+  std::unique_ptr<WorkletGlobalScopeProxy> proxy =
+      WTF::MakeUnique<PaintWorkletGlobalScopeProxy>(frame_);
+  global_scope_proxies_.insert(std::move(proxy));
+}
+
 }  // namespace blink