setupDefultFontManager correctly clear out cache

third_party/txt/BUILD.gn

@@ -141,11 +141,17 @@ if (enable_unittests) {
   executable("txt_unittests") {
     testonly = true
 
-    sources = [ "tests/txt_run_all_unittests.cc" ]
+    sources = [
+      "tests/font_collection_tests.cc",
+      "tests/txt_run_all_unittests.cc",
+    ]
+
+    public_configs = [ ":txt_config" ]
 
     configs += [ ":allow_posix_names" ]
 
     deps = [
+      ":txt",
       ":txt_fixtures",
       "//flutter/fml",
       "//flutter/testing:testing_lib",

third_party/txt/src/txt/font_collection.cc

@@ -46,6 +46,7 @@ size_t FontCollection::GetFontManagersCount() const {
 void FontCollection::SetupDefaultFontManager(
     uint32_t font_initialization_data) {
   default_font_manager_ = GetDefaultFontManager(font_initialization_data);
+  skt_collection_.reset();
 }
 
 void FontCollection::SetDefaultFontManager(sk_sp<SkFontMgr> font_manager) {

third_party/txt/tests/font_collection_tests.cc

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2017 Google, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "gtest/gtest.h"
+
+#include <sstream>
+
+#include "txt/font_collection.h"
+
+namespace txt {
+namespace testing {
+
+class FontCollectionTests : public ::testing::Test {
+ public:
+  FontCollectionTests() {}
+
+  void SetUp() override {}
+};
+
+TEST_F(FontCollectionTests, SettingUpDefaultFontManagerClearsCache) {
+  FontCollection font_collection;
+  sk_sp<skia::textlayout::FontCollection> sk_font_collection =
+      font_collection.CreateSktFontCollection();
+  ASSERT_EQ(sk_font_collection->getFallbackManager().get(), nullptr);
+  font_collection.SetupDefaultFontManager(0);
+  sk_font_collection = font_collection.CreateSktFontCollection();
+  ASSERT_NE(sk_font_collection->getFallbackManager().get(), nullptr);
+}
+}  // namespace testing
+}  // namespace txt