Don't default-construct std::strings and then assign them.

Change-Id: I8c994d1e6a8d2ebe52eaa4f0132e0deb2ecfa5f3
diff --git a/src/compiler/Frontend.cc b/src/compiler/Frontend.cc
index 75f5d7d..ba5bd3d 100644
--- a/src/compiler/Frontend.cc
+++ b/src/compiler/Frontend.cc
@@ -215,7 +215,7 @@
 void oatDumpCFG(CompilationUnit* cUnit, const char* dirPrefix)
 {
     FILE* file;
-    std::string name = art::PrettyMethod(cUnit->method_idx, *cUnit->dex_file);
+    std::string name(art::PrettyMethod(cUnit->method_idx, *cUnit->dex_file));
     char startOffset[80];
     sprintf(startOffset, "_%x", cUnit->entryBlock->fallThrough->startOffset);
     char* fileName = (char*) oatNew(