Add dependency to gflags and related tests

WORKSPACE

@@ -15,3 +15,11 @@ new_http_archive(
     build_file = "third_party/gtest.BUILD",
     strip_prefix = "googletest-release-1.7.0",
 )
+
+# External dependency to gflags.  This method comes from
+# https://github.com/gflags/example/blob/master/WORKSPACE.
+git_repository(
+    name   = "gflags",
+    tag    = "v2.2.0",
+    remote = "https://github.com/gflags/gflags.git"
+)

third_party/gflags_test/BUILD

+licenses(["notice"])  # Apache 2.0
+
+cc_test(
+    name = "gflags_test",
+    srcs = ["gflags_test.cc"],
+    copts = ["-Iexternal/gtest/include"],
+    deps = [
+        "@gtest//:main",
+        "@gflags//:gflags",
+     ],
+)

third_party/gflags_test/gflags_test.cc

+#include <iostream>
+#include <string>
+
+#include "gflags/gflags.h"
+#include "gtest/gtest.h"
+
+
+DEFINE_bool(verbose, false, "Display program name before message");
+DEFINE_string(message, "Hello world!", "Message to print");
+
+static bool IsNonEmptyMessage(const char *flagname, const std::string &value)
+{
+  return value[0] != '\0';
+}
+DEFINE_validator(message, &IsNonEmptyMessage);
+
+
+namespace third_party {
+namespace gflags_test {
+
+TEST(GflagsTest, ParseAndPrint) {
+  gflags::SetUsageMessage("some usage message");
+  gflags::SetVersionString("1.0.0");
+  int argc = 1;
+  char program_name[] = "gflags_test";
+  char** argv = new char*[2];
+  argv[0] = program_name;
+  argv[1] = NULL;
+  gflags::ParseCommandLineFlags(&argc, reinterpret_cast<char***>(&argv), true);
+  EXPECT_EQ("gflags_test", std::string(gflags::ProgramInvocationShortName()));
+  EXPECT_EQ("Hello world!", FLAGS_message);
+  gflags::ShutDownCommandLineFlags();
+}
+
+}  // namespace gflags_test
+}  // namespace third_party