Fix logFormat

Summary: Ooops during port ;)

Test Plan: unit test

Reviewed By: agoder@fb.com

Subscribers: trunkagent, folly-diffs@, yfeldblum

FB internal diff: D1905639

Signature: t1:1905639:1426171227:a6e415046a85f098ac090f069476204fb0367c42

folly/experimental/AutoTimer.h

@@ -94,7 +94,7 @@ public:
   template<typename... Args>
   double logFormat(Args&&... args) {
     auto now = Clock::now();
-    return logImpl(now, format(std::forward<Args>(args)...));
+    return logImpl(now, format(std::forward<Args>(args)...).str());
   }
 
 private:

folly/experimental/test/AutoTimerTest.cpp

@@ -50,6 +50,9 @@ TEST(TestAutoTimer, HandleBasic) {
   timer.log("foo");
   ASSERT_EQ("foo", StubLogger::m);
   ASSERT_EQ(2, StubLogger::t);
+  timer.logFormat("bar {}", 5e-2);
+  ASSERT_EQ("bar 0.05", StubLogger::m);
+  ASSERT_EQ(0, StubLogger::t);
 }
 
 TEST(TestAutoTimer, HandleLogOnDestruct) {