Make the GL context current in EmbedderSurfaceGLImpeller before creating the GPU surface (#50807)

The GPUSurfaceGLImpeller ctor creates an AiksContext/ContentContext, which loads the shader pipelines.  If the current thread does not have a GL context and can not execute ReactorGLES operations, then the pipeline futures will not complete.  This can cause the raster thread to hang if the reactor has not run and the futures are still incomplete when a rendering task later needs to obtain the pipeline.

Author: jason-simmons

shell/platform/embedder/BUILD.gn

@@ -242,7 +242,7 @@ test_fixtures("fixtures") {
     "fixtures/dpr_noxform.png",
     "fixtures/dpr_xform.png",
     "fixtures/gradient.png",
-    "fixtures/impeller_gl_gradient.png",
+    "fixtures/impeller_gl_test.png",
     "fixtures/vk_dpr_noxform.png",
     "fixtures/vk_gradient.png",
     "fixtures/gradient_metal.png",

shell/platform/embedder/embedder_surface_gl_impeller.cc

@@ -178,6 +178,11 @@ EmbedderSurfaceGLImpeller::GLContextFramebufferInfo() const {
 
 // |EmbedderSurface|
 std::unique_ptr<Surface> EmbedderSurfaceGLImpeller::CreateGPUSurface() {
+  // Ensure that the GL context is current before creating the GPU surface.
+  // GPUSurfaceGLImpeller initialization will set up shader pipelines, and the
+  // current thread needs to be able to execute reactor operations.
+  GLContextMakeCurrent();
+
   return std::make_unique<GPUSurfaceGLImpeller>(
       this,                     // GPU surface GL delegate
       impeller_context_,        // Impeller context

shell/platform/embedder/fixtures/impeller_gl_gradient.png

@@ -1364,3 +1364,21 @@ void render_gradient_retained() {
   };
   PlatformDispatcher.instance.scheduleFrame();
 }
+
+@pragma('vm:entry-point')
+void render_impeller_gl_test() {
+  PlatformDispatcher.instance.onBeginFrame = (Duration duration) {
+    final SceneBuilder builder = SceneBuilder();
+    builder.pushOffset(0.0, 0.0);
+    final Paint paint = Paint();
+    paint.color = Color.fromARGB(255, 0, 0, 255);
+    final PictureRecorder baseRecorder = PictureRecorder();
+    final Canvas canvas = Canvas(baseRecorder);
+    canvas.drawPaint(Paint()..color = Color.fromARGB(255, 255, 0, 0));
+    canvas.drawRect(Rect.fromLTRB(20.0, 20.0, 200.0, 150.0), paint);
+    builder.addPicture(Offset.zero, baseRecorder.endRecording());
+    builder.pop();
+    PlatformDispatcher.instance.views.first.render(builder.build());
+  };
+  PlatformDispatcher.instance.scheduleFrame();
+}

shell/platform/embedder/fixtures/impeller_gl_test.png

@@ -4711,7 +4711,7 @@ TEST_F(EmbedderTest, CanRenderWithImpellerOpenGL) {
       });
 
   builder.AddCommandLineArgument("--enable-impeller");
-  builder.SetDartEntrypoint("render_gradient");
+  builder.SetDartEntrypoint("render_impeller_gl_test");
   builder.SetOpenGLRendererConfig(SkISize::Make(800, 600));
   builder.SetCompositor();
   builder.SetRenderTargetType(
@@ -4733,7 +4733,7 @@ TEST_F(EmbedderTest, CanRenderWithImpellerOpenGL) {
 
   ASSERT_TRUE(ImageMatchesFixture(
       FixtureNameForBackend(EmbedderTestContextType::kOpenGLContext,
-                            "impeller_gl_gradient.png"),
+                            "impeller_gl_test.png"),
       rendered_scene));
 
   // The scene will be rendered by the compositor, and the surface present