[Linux] Fix a race between the Flutter renderer vs. FlGlArea size alloc

shell/platform/linux/BUILD.gn

@@ -224,6 +224,7 @@ executable("flutter_linux_unittests") {
     "fl_texture_registrar_test.cc",
     "fl_value_test.cc",
     "fl_view_accessible_test.cc",
+    "fl_view_test.cc",
     "testing/fl_test.cc",
     "testing/mock_binary_messenger.cc",
     "testing/mock_binary_messenger_response_handle.cc",

shell/platform/linux/fl_view.cc

@@ -724,6 +724,26 @@ static void fl_view_get_preferred_height(GtkWidget* widget,
   }
 }
 
+static void size_allocate_child(FlView* view,
+                                FlViewChild* child,
+                                GtkAllocation* allocation) {
+  GtkAllocation child_allocation = child->geometry;
+  GtkRequisition child_requisition;
+  gtk_widget_get_preferred_size(child->widget, &child_requisition, NULL);
+
+  if (!gtk_widget_get_has_window(GTK_WIDGET(view))) {
+    child_allocation.x += allocation->x;
+    child_allocation.y += allocation->y;
+  }
+
+  if (child_allocation.width == 0 && child_allocation.height == 0) {
+    child_allocation.width = allocation->width;
+    child_allocation.height = allocation->height;
+  }
+
+  gtk_widget_size_allocate(child->widget, &child_allocation);
+}
+
 // Implements GtkWidget::size-allocate.
 static void fl_view_size_allocate(GtkWidget* widget,
                                   GtkAllocation* allocation) {
@@ -746,21 +766,7 @@ static void fl_view_size_allocate(GtkWidget* widget,
       continue;
     }
 
-    GtkAllocation child_allocation = child->geometry;
-    GtkRequisition child_requisition;
-    gtk_widget_get_preferred_size(child->widget, &child_requisition, NULL);
-
-    if (!gtk_widget_get_has_window(widget)) {
-      child_allocation.x += allocation->x;
-      child_allocation.y += allocation->y;
-    }
-
-    if (child_allocation.width == 0 && child_allocation.height == 0) {
-      child_allocation.width = allocation->width;
-      child_allocation.height = allocation->height;
-    }
-
-    gtk_widget_size_allocate(child->widget, &child_allocation);
+    size_allocate_child(self, child, allocation);
   }
 
   GtkAllocation event_box_allocation = {
@@ -978,6 +984,9 @@ void fl_view_add_widget(FlView* view,
 }
 
 void fl_view_end_frame(FlView* view) {
+  GtkAllocation allocation;
+  gtk_widget_get_allocation(GTK_WIDGET(view), &allocation);
+
   for (GList* pending_child = view->pending_children_list; pending_child;
        pending_child = pending_child->next) {
     FlViewChild* pending_view_child =
@@ -991,6 +1000,7 @@ void fl_view_end_frame(FlView* view) {
     } else {
       // newly added child
       gtk_widget_set_parent(pending_view_child->widget, GTK_WIDGET(view));
+      size_allocate_child(view, pending_view_child, &allocation);
     }
   }
 

shell/platform/linux/fl_view_test.cc

@@ -0,0 +1,49 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Included first as it collides with the X11 headers.
+#include "gtest/gtest.h"
+
+#include "flutter/shell/platform/linux/fl_view_private.h"
+#include "flutter/shell/platform/linux/public/flutter_linux/fl_engine.h"
+#include "flutter/shell/platform/linux/public/flutter_linux/fl_view.h"
+#include "flutter/shell/platform/linux/testing/fl_test.h"
+
+struct FlViewTest : ::testing::Test {
+  static void SetUpTestSuite() { gtk_init(nullptr, nullptr); }
+};
+
+TEST_F(FlViewTest, SizeAllocate) {
+  g_autoptr(FlDartProject) project = fl_dart_project_new();
+  FlView* view = fl_view_new(project);
+  gtk_widget_show(GTK_WIDGET(view));
+
+  GtkAllocation allocation = {0, 0, 320, 240};
+  gtk_widget_size_allocate(GTK_WIDGET(view), &allocation);
+
+  fl_view_begin_frame(view);
+
+  GtkWidget* child = gtk_label_new(nullptr);
+  fl_view_add_widget(view, child, nullptr);
+
+  fl_view_end_frame(view);
+
+  GtkAllocation child_allocation;
+  gtk_widget_get_allocation(child, &child_allocation);
+  EXPECT_EQ(child_allocation.x, 0);
+  EXPECT_EQ(child_allocation.y, 0);
+  EXPECT_EQ(child_allocation.width, 320);
+  EXPECT_EQ(child_allocation.height, 240);
+
+  allocation = {0, 0, 321, 239};
+  gtk_widget_size_allocate(GTK_WIDGET(view), &allocation);
+
+  gtk_widget_get_allocation(child, &child_allocation);
+  EXPECT_EQ(child_allocation.x, 0);
+  EXPECT_EQ(child_allocation.y, 0);
+  EXPECT_EQ(child_allocation.width, 321);
+  EXPECT_EQ(child_allocation.height, 239);
+
+  gtk_widget_destroy(GTK_WIDGET(view));
+}