Implement clang tool that converts std::string("") to std::string().

tools/clang/empty_string/tests/test-expected.cc

Index: tools/clang/empty_string/tests/test-expected.cc
diff --git a/tools/clang/empty_string/tests/test-expected.cc b/tools/clang/empty_string/tests/test-expected.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8862d9fdad3244970c6fd40f1599e53e2eacd127
--- /dev/null
+++ b/tools/clang/empty_string/tests/test-expected.cc
@@ -0,0 +1,34 @@
+// Test file for the empty string clang tool.
+
+#include <string>
+
+// Tests for std::string declarations.
+void TestDeclarations() { std::string a, b("abc"), c; }
+
+// Tests for std::string allocated with new.
+void TestNew() {
+  std::string* a = new std::string,
+              *b = new std::string("abc"),
+              *c = new std::string,
+              *d = new std::string();
+}
+
+// Tests for std::string construction in initializer lists.
+class TestInitializers {
+ public:
+  TestInitializers()  {}
+  TestInitializers(bool)  {}
+  TestInitializers(double) :  b("cat"), c() {}
+
+ private:
+  std::string a;
+  std::string b;
+  std::string c;
+};
+
+// Tests for temporary std::strings.
+void TestTemporaries(const std::string& reference_argument,
+                     const std::string value_argument) {
+  TestTemporaries(std::string(), std::string());
+  TestTemporaries(std::string(), std::string());
+}