Added new ReadFileToString API with a max_size argument

base/file_util_unittest.cc

Index: base/file_util_unittest.cc
diff --git a/base/file_util_unittest.cc b/base/file_util_unittest.cc
index d3c246e42928675bcf08a9e0b242294ba58a30e6..0c0dbbc54fe1dbb3bc906a67aba6b6d23f93b431 100644
--- a/base/file_util_unittest.cc
+++ b/base/file_util_unittest.cc
@@ -1924,6 +1924,48 @@ TEST_F(FileUtilTest, AppendToFile) {
   EXPECT_EQ(L"hellohello", read_content);
 }
 
+TEST_F(FileUtilTest, ReadFileToString) {
+  const char kTestData[] = "0123";
+  std::string data;
+
+  FilePath file_path =
+      temp_dir_.path().Append(FILE_PATH_LITERAL("ReadFileToStringTest"));
+
+  ASSERT_EQ(4, file_util::WriteFile(file_path, kTestData, 4));
+
+  EXPECT_TRUE(ReadFileToString(file_path, &data));
+  EXPECT_EQ(kTestData, data);
+
+  data.clear();
+  EXPECT_FALSE(ReadFileToString(file_path, &data, 0));
+  EXPECT_EQ(data.length(), 0u);
+
+  data.clear();
+  EXPECT_FALSE(ReadFileToString(file_path, &data, 2));
+  EXPECT_EQ("01", data);
+
+  data.clear();
+  EXPECT_FALSE(ReadFileToString(file_path, &data, 3));
+  EXPECT_EQ("012", data);
+
+  data.clear();
+  EXPECT_TRUE(ReadFileToString(file_path, &data, 4));
+  EXPECT_EQ("0123", data);
+
+  data.clear();
+  EXPECT_TRUE(ReadFileToString(file_path, &data, 6));
+  EXPECT_EQ("0123", data);
+
+  EXPECT_TRUE(ReadFileToString(file_path, NULL, 6));
+
+  EXPECT_TRUE(ReadFileToString(file_path, NULL));
+
+  EXPECT_TRUE(base::DeleteFile(file_path, false));
+
+  EXPECT_FALSE(ReadFileToString(file_path, &data));
+  EXPECT_FALSE(ReadFileToString(file_path, &data, 6));
+}
+
 TEST_F(FileUtilTest, TouchFile) {
   FilePath data_dir =
       temp_dir_.path().Append(FILE_PATH_LITERAL("FilePathTest"));