Use ErrorOr for the ::create factory on instrumented and sample profilers.

Summary:
As discussed in
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20141027/242445.html,
the creation of reader and writer instances is better done using
ErrorOr. There are no functional changes, but several callers needed to
be adjusted.

Reviewers: bogner

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D6076

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221120 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ProfileData/SampleProfReader.h

@@ -92,9 +92,8 @@ public:
   }
 
   /// \brief Create a sample profile reader appropriate to the file format.
-  static std::error_code create(StringRef Filename,
-                                std::unique_ptr<SampleProfileReader> &Reader,
-                                LLVMContext &C);
+  static ErrorOr<std::unique_ptr<SampleProfileReader>>
+  create(StringRef Filename, LLVMContext &C);
 
 protected:
   /// \brief Map every function to its associated profile.