Make tooling::applyAllReplacements return llvm::Expected<string> instead of empty string to indicate potential error.

Summary:
return llvm::Expected<> to carry error status and error information.
This is the first step towards introducing "Error" into tooling::Replacements.

Reviewers: djasper, klimek

Subscribers: ioeric, klimek, cfe-commits

Differential Revision: http://reviews.llvm.org/D21601

llvm-svn: 275062
diff --git a/clang/unittests/Format/FormatTestSelective.cpp b/clang/unittests/Format/FormatTestSelective.cpp
index c4286d4..2bc60fd 100644
--- a/clang/unittests/Format/FormatTestSelective.cpp
+++ b/clang/unittests/Format/FormatTestSelective.cpp
@@ -28,10 +28,10 @@
     tooling::Replacements Replaces =
         reformat(Style, Code, Ranges, "<stdin>", &IncompleteFormat);
     EXPECT_FALSE(IncompleteFormat) << Code << "\n\n";
-    std::string Result = applyAllReplacements(Code, Replaces);
-    EXPECT_NE("", Result);
-    DEBUG(llvm::errs() << "\n" << Result << "\n\n");
-    return Result;
+    auto Result = applyAllReplacements(Code, Replaces);
+    EXPECT_TRUE(static_cast<bool>(Result));
+    DEBUG(llvm::errs() << "\n" << *Result << "\n\n");
+    return *Result;
   }
 
   FormatStyle Style = getLLVMStyle();