Reduce StringPiece usage a bit.

Various easy cases, in case we want to move towards making the StringPiece
constructors explicit.

Change-Id: I49e5efc5b787f847ab4cb12d66d1d16aed03fa67
diff --git a/src/jni_internal.cc b/src/jni_internal.cc
index 0921afb..8b61226 100644
--- a/src/jni_internal.cc
+++ b/src/jni_internal.cc
@@ -2668,8 +2668,7 @@
   Runtime::Options options;
   for (int i = 0; i < args->nOptions; ++i) {
     JavaVMOption* option = &args->options[i];
-    options.push_back(std::make_pair(StringPiece(option->optionString),
-                                     option->extraInfo));
+    options.push_back(std::make_pair(std::string(option->optionString), option->extraInfo));
   }
   bool ignore_unrecognized = args->ignoreUnrecognized;
   Runtime* runtime = Runtime::Create(options, ignore_unrecognized);