Introduce a new framework for back-and-forth tracked/protected preferences migration.

base/files/important_file_writer_unittest.cc

Index: base/files/important_file_writer_unittest.cc
diff --git a/base/files/important_file_writer_unittest.cc b/base/files/important_file_writer_unittest.cc
index 02a5f76b2b6e7a9d775d4b0f4551d205a2aa4c8d..3f62fe4953b8f1792df05a7d065863dad20e093f 100644
--- a/base/files/important_file_writer_unittest.cc
+++ b/base/files/important_file_writer_unittest.cc
@@ -4,6 +4,7 @@
 
 #include "base/files/important_file_writer.h"
 
+#include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/file_util.h"
 #include "base/files/file_path.h"
@@ -41,6 +42,41 @@ class DataSerializer : public ImportantFileWriter::DataSerializer {
   const std::string data_;
 };
 
+class SuccessfulWriteObserver {
+ public:
+  SuccessfulWriteObserver() : successful_write_observed_(false) {}
+
+  // Register on_successful_write() to be called on the next successful write
+  // of |writer|.
+  void ObserveNextSuccessfulWrite(ImportantFileWriter* writer);
+
+  // Returns true if a successful write was observed via on_successful_write()
+  // and resets the observation state to false regardless.
+  bool GetAndResetObservationState();
+
+ private:
+  void on_successful_write() {
+    EXPECT_FALSE(successful_write_observed_);
+    successful_write_observed_ = true;
+  }
+
+  bool successful_write_observed_;
+
+  DISALLOW_COPY_AND_ASSIGN(SuccessfulWriteObserver);
+};
+
+void SuccessfulWriteObserver::ObserveNextSuccessfulWrite(
+    ImportantFileWriter* writer) {
+  writer->RegisterOnNextSuccessfulWriteCallback(base::Bind(
+      &SuccessfulWriteObserver::on_successful_write, base::Unretained(this)));
+}
+
+bool SuccessfulWriteObserver::GetAndResetObservationState() {
+  bool was_successful_write_observed = successful_write_observed_;
+  successful_write_observed_ = false;
+  return was_successful_write_observed;
+}
+
 }  // namespace
 
 class ImportantFileWriterTest : public testing::Test {
@@ -52,6 +88,7 @@ class ImportantFileWriterTest : public testing::Test {
   }
 
  protected:
+  SuccessfulWriteObserver successful_write_observer_;
   FilePath file_;
   MessageLoop loop_;
 
@@ -62,11 +99,47 @@ class ImportantFileWriterTest : public testing::Test {
 TEST_F(ImportantFileWriterTest, Basic) {
   ImportantFileWriter writer(file_, MessageLoopProxy::current().get());
   EXPECT_FALSE(PathExists(writer.path()));
+  EXPECT_FALSE(successful_write_observer_.GetAndResetObservationState());
+  writer.WriteNow("foo");
+  RunLoop().RunUntilIdle();
+
+  EXPECT_FALSE(successful_write_observer_.GetAndResetObservationState());
+  ASSERT_TRUE(PathExists(writer.path()));
+  EXPECT_EQ("foo", GetFileContent(writer.path()));
+}
+
+TEST_F(ImportantFileWriterTest, BasicWithSuccessfulWriteObserver) {
+  ImportantFileWriter writer(file_, MessageLoopProxy::current().get());
+  EXPECT_FALSE(PathExists(writer.path()));
+  EXPECT_FALSE(successful_write_observer_.GetAndResetObservationState());
+  successful_write_observer_.ObserveNextSuccessfulWrite(&writer);
   writer.WriteNow("foo");
   RunLoop().RunUntilIdle();
 
+  // Confirm that the observer is invoked.
+  EXPECT_TRUE(successful_write_observer_.GetAndResetObservationState());
   ASSERT_TRUE(PathExists(writer.path()));
   EXPECT_EQ("foo", GetFileContent(writer.path()));
+
+  // Confirm that re-installing the observer works for another write.
+  EXPECT_FALSE(successful_write_observer_.GetAndResetObservationState());
+  successful_write_observer_.ObserveNextSuccessfulWrite(&writer);
+  writer.WriteNow("bar");
+  RunLoop().RunUntilIdle();
+
+  EXPECT_TRUE(successful_write_observer_.GetAndResetObservationState());
+  ASSERT_TRUE(PathExists(writer.path()));
+  EXPECT_EQ("bar", GetFileContent(writer.path()));
+
+  // Confirm that writing again without re-installing the observer doesn't
+  // result in a notification.
+  EXPECT_FALSE(successful_write_observer_.GetAndResetObservationState());
+  writer.WriteNow("baz");
+  RunLoop().RunUntilIdle();
+
+  EXPECT_FALSE(successful_write_observer_.GetAndResetObservationState());
+  ASSERT_TRUE(PathExists(writer.path()));
+  EXPECT_EQ("baz", GetFileContent(writer.path()));
 }
 
 TEST_F(ImportantFileWriterTest, ScheduleWrite) {