Correct the OffscreenCanvas.getContext API

third_party/WebKit/Source/modules/webgl/WebGL2RenderingContext.cpp

Index: third_party/WebKit/Source/modules/webgl/WebGL2RenderingContext.cpp
diff --git a/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContext.cpp b/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContext.cpp
index db5216fa3ecb5d55548c2f258e795b169a6c2503..01141e5be87a6d36335777e5e7577648fa1d4628 100644
--- a/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContext.cpp
+++ b/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContext.cpp
@@ -34,29 +34,45 @@
 
 namespace blink {
 
-CanvasRenderingContext* WebGL2RenderingContext::Factory::create(
-    HTMLCanvasElement* canvas,
-    const CanvasContextCreationAttributes& attrs,
-    Document&) {
-  std::unique_ptr<WebGraphicsContext3DProvider> contextProvider(
-      createWebGraphicsContext3DProvider(canvas, attrs, 2));
+// An helper function for the two create() methods. The return value is an
+// indicate of whether the create() should return nullptr or not.
+static bool shouldCreateContext(WebGraphicsContext3DProvider* contextProvider,
+                                HTMLCanvasElement* canvas,
+                                OffscreenCanvas* offscreenCanvas) {
   if (!contextProvider) {
-    canvas->dispatchEvent(WebGLContextEvent::create(
-        EventTypeNames::webglcontextcreationerror, false, true,
-        "Failed to create a WebGL2 context."));
-    return nullptr;
+    if (canvas) {
+      canvas->dispatchEvent(WebGLContextEvent::create(
+          EventTypeNames::webglcontextcreationerror, false, true,
+          "Failed to create a WebGL2 context."));
+    } else {
+      offscreenCanvas->dispatchEvent(WebGLContextEvent::create(
+          EventTypeNames::webglcontextcreationerror, false, true,
+          "Failed to create a WebGL2 context."));
+    }
+    return false;
   }
+
   gpu::gles2::GLES2Interface* gl = contextProvider->contextGL();
   std::unique_ptr<Extensions3DUtil> extensionsUtil =
       Extensions3DUtil::create(gl);
   if (!extensionsUtil)
-    return nullptr;
+    return false;
   if (extensionsUtil->supportsExtension("GL_EXT_debug_marker")) {
     String contextLabel(
-        String::format("WebGL2RenderingContext-%p", contextProvider.get()));
+        String::format("WebGL2RenderingContext-%p", contextProvider));
     gl->PushGroupMarkerEXT(0, contextLabel.ascii().data());
   }
+  return true;
+}
 
+CanvasRenderingContext* WebGL2RenderingContext::Factory::create(
+    HTMLCanvasElement* canvas,
+    const CanvasContextCreationAttributes& attrs,
+    Document&) {
+  std::unique_ptr<WebGraphicsContext3DProvider> contextProvider(
+      createWebGraphicsContext3DProvider(canvas, attrs, 2));
+  if (!shouldCreateContext(contextProvider.get(), canvas, nullptr))
+    return nullptr;
   WebGL2RenderingContext* renderingContext =
       new WebGL2RenderingContext(canvas, std::move(contextProvider), attrs);
 
@@ -73,6 +89,30 @@ CanvasRenderingContext* WebGL2RenderingContext::Factory::create(
   return renderingContext;
 }
 
+CanvasRenderingContext* WebGL2RenderingContext::Factory::create(
+    ScriptState* scriptState,
+    OffscreenCanvas* offscreenCanvas,
+    const CanvasContextCreationAttributes& attrs) {
+  std::unique_ptr<WebGraphicsContext3DProvider> contextProvider(
+      createWebGraphicsContext3DProvider(scriptState, attrs, 2));
+  if (!shouldCreateContext(contextProvider.get(), nullptr, offscreenCanvas))
+    return nullptr;
+  WebGL2RenderingContext* renderingContext = new WebGL2RenderingContext(
+      offscreenCanvas, std::move(contextProvider), attrs);
+
+  if (!renderingContext->drawingBuffer()) {
+    offscreenCanvas->dispatchEvent(WebGLContextEvent::create(
+        EventTypeNames::webglcontextcreationerror, false, true,
+        "Could not create a WebGL2 context."));
+    return nullptr;
+  }
+
+  renderingContext->initializeNewContext();
+  renderingContext->registerContextExtensions();
+
+  return renderingContext;
+}
+
 void WebGL2RenderingContext::Factory::onError(HTMLCanvasElement* canvas,
                                               const String& error) {
   canvas->dispatchEvent(WebGLContextEvent::create(
@@ -87,6 +127,14 @@ WebGL2RenderingContext::WebGL2RenderingContext(
                                  std::move(contextProvider),
                                  requestedAttributes) {}
 
+WebGL2RenderingContext::WebGL2RenderingContext(
+    OffscreenCanvas* passedOffscreenCanvas,
+    std::unique_ptr<WebGraphicsContext3DProvider> contextProvider,
+    const CanvasContextCreationAttributes& requestedAttributes)
+    : WebGL2RenderingContextBase(passedOffscreenCanvas,
+                                 std::move(contextProvider),
+                                 requestedAttributes) {}
+
 WebGL2RenderingContext::~WebGL2RenderingContext() {}
 
 void WebGL2RenderingContext::setCanvasGetContextResult(