Provide the skia_vulkan_header variable now required by Skia's Vulkan…

… build scripts (flutter#4459)

tools/gn

@@ -162,7 +162,7 @@ def to_gn_args(args):
       gn_args['shell_enable_vulkan'] = True
       # Configure Skia for Vulkan support.
       gn_args['skia_use_vulkan'] = True
-      gn_args['skia_vulkan_headers'] = "//third_party/vulkan/src"
+      gn_args['skia_vulkan_header'] = "flutter/vulkan/skia_vulkan_header.h"
 
     # We should not need a special case for x86, but this seems to introduce text relocations
     # even with -fPIC everywhere.

travis/licenses_golden/licenses_flutter

@@ -1220,6 +1220,7 @@ FILE: ../../../flutter/third_party/txt/src/txt/platform.cc
 FILE: ../../../flutter/third_party/txt/src/txt/platform.h
 FILE: ../../../flutter/third_party/txt/src/txt/platform_android.cc
 FILE: ../../../flutter/third_party/txt/src/txt/platform_mac.mm
+FILE: ../../../flutter/vulkan/skia_vulkan_header.h
 FILE: ../../../flutter/vulkan/vulkan_native_surface_magma.cc
 FILE: ../../../flutter/vulkan/vulkan_native_surface_magma.h
 ----------------------------------------------------------------------------------------------------

vulkan/skia_vulkan_header.h

@@ -0,0 +1,11 @@
+// Copyright 2017 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.
+
+#ifdef __ANDROID__
+#ifndef VK_USE_PLATFORM_ANDROID_KHR
+#define VK_USE_PLATFORM_ANDROID_KHR 1
+#endif  // VK_USE_PLATFORM_ANDROID_KHR
+#endif  // __ANDROID__
+
+#include "third_party/vulkan/src/vulkan/vulkan.h"