Introduce CSSAssertSetFailFunc and CSSAsserFail to throw managed exception

Summary:
- Define CSS_ASSERT_FAIL_ENABLED for P/Invoke (Visual Studio project already has it)
- Pass managed delegate pointer to unmanaged side via P/Invoke.
- CSSAssertFail will call the managed delegate when assert failed.
- The delegate will throw managed exception.

Reviewed By: emilsjolander

Differential Revision: D3982084

fbshipit-source-id: 058a87c10ca89238362be4d8759cc00dd0c9b376

csharp/Facebook.CSSLayout/CSSAssert.cs

@@ -0,0 +1,31 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+using System;
+
+namespace Facebook.CSSLayout
+{
+    internal static class CSSAssert
+    {
+        public delegate void FailFunc(string message);
+
+        private static bool _assertInitialized;
+
+        public static void Initialize()
+        {
+            if (!_assertInitialized)
+            {
+                Native.CSSAssertSetFailFunc((message) => {
+                    throw new InvalidOperationException(message);
+                });
+                _assertInitialized = true;
+            }
+        }
+    }
+}

csharp/Facebook.CSSLayout/CSSNode.cs

@@ -93,6 +93,7 @@ namespace Facebook.CSSLayout
                 throw new InvalidOperationException("Allready initialized node");
             }
 
+            CSSAssert.Initialize();
             _cssNode = Native.CSSNodeNew();
             _children = new List<CSSNode>(4);
             Native.CSSNodeSetPrintFunc(_cssNode, _printFunc);

csharp/Facebook.CSSLayout/Native.cs

@@ -20,6 +20,9 @@ namespace Facebook.CSSLayout
         private const string DllName = "CSSLayout";
 #endif
 
+        [DllImport(DllName)]
+        public static extern void CSSAssertSetFailFunc(CSSAssert.FailFunc func);
+
         [DllImport(DllName)]
         public static extern IntPtr CSSNodeNew();