Fix error reporting in the PNaCl bitcode reader.

include/llvm/Bitcode/NaCl/NaClReaderWriter.h

Index: include/llvm/Bitcode/NaCl/NaClReaderWriter.h
diff --git a/include/llvm/Bitcode/NaCl/NaClReaderWriter.h b/include/llvm/Bitcode/NaCl/NaClReaderWriter.h
index 4b92e4767c21d501c6e4f966ff42cc341554ca3e..78ceddce6c278f5629bce9690990b9890379cd79 100644
--- a/include/llvm/Bitcode/NaCl/NaClReaderWriter.h
+++ b/include/llvm/Bitcode/NaCl/NaClReaderWriter.h
@@ -17,6 +17,7 @@
 #define LLVM_BITCODE_NACL_NACLREADERWRITER_H
 
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/ErrorOr.h"
 
 #include <string>
 
@@ -44,9 +45,11 @@ namespace llvm {
 
   /// getNaClLazyBitcodeModule - Read the header of the specified bitcode buffer
   /// and prepare for lazy deserialization of function bodies.  If successful,
-  /// this takes ownership of 'buffer' and returns a non-null pointer.  On
-  /// error, this returns null, *does not* take ownership of Buffer, and fills
-  /// in *ErrMsg with an error description if ErrMsg is non-null.
+  /// takes ownership of 'buffer' and returns a non-null pointer.  On
+  /// error, this returns an error code and *does not* take ownership of Buffer.
+  ///
+  /// When Verbose is non-null, more descriptive error messages are also
+  /// written to Verbose.
   ///
   /// The AcceptSupportedOnly argument is used to decide which PNaCl versions
   /// of the PNaCl bitcode to accept. There are three forms:
@@ -56,34 +59,38 @@ namespace llvm {
   ///    3) Unreadable.
   /// When AcceptSupportedOnly is true, only form 1 is allowed. When
   /// AcceptSupportedOnly is false, forms 1 and 2 are allowed.
-  Module *getNaClLazyBitcodeModule(MemoryBuffer *Buffer,
-                                   LLVMContext &Context,
-                                   std::string *ErrMsg = 0,
-                                   bool AcceptSupportedOnly = true);
+  ErrorOr<Module *> getNaClLazyBitcodeModule(MemoryBuffer *Buffer,
+                                             LLVMContext &Context,
+                                             raw_ostream *Verbose = nullptr,
+                                             bool AcceptSupportedOnly = true);
 
   /// getNaClStreamedBitcodeModule - Read the header of the specified stream
   /// and prepare for lazy deserialization and streaming of function bodies.
   /// On error, this returns null, and fills in *ErrMsg with an error
   /// description if ErrMsg is non-null.
   ///
-  /// See getNaClLazyBitcodeModule for an explanation of argument
-  /// AcceptSupportedOnly.
+  /// See getNaClLazyBitcodeModule for an explanation of arguments
+  /// Verbose, AcceptSupportedOnly.
+  /// TODO(kschimpf): Refactor this and getStreamedBitcodeModule to use
+  /// ErrorOr<Module *> API so that all methods have the same interface.
   Module *getNaClStreamedBitcodeModule(const std::string &name,
                                        StreamingMemoryObject *streamer,
                                        LLVMContext &Context,
-                                       std::string *ErrMsg = 0,
+                                       raw_ostream *Verbose = nullptr,
+                                       std::string *ErrMsg = nullptr,
                                        bool AcceptSupportedOnly = true);
 
   /// NaClParseBitcodeFile - Read the specified bitcode file,
-  /// returning the module.  If an error occurs, this returns null and
-  /// fills in *ErrMsg if it is non-null.  This method *never* takes
-  /// ownership of Buffer.
+  /// returning the module.  If successful, takes ownership of
+  /// 'buffer' and returns a non-null pointer.  On error, this returns
+  /// an error code and *does not* take ownership of Buffer.
   ///
-  /// See getNaClLazyBitcodeModule for an explanation of argument
-  /// AcceptSupportedOnly.
-  Module *NaClParseBitcodeFile(MemoryBuffer *Buffer, LLVMContext &Context,
-                               std::string *ErrMsg = 0,
-                               bool AcceptSupportedOnly = true);
+  /// See getNaClLazyBitcodeModule for an explanation of arguments
+  /// Verbose, AcceptSupportedOnly.
+  ErrorOr<Module *> NaClParseBitcodeFile(MemoryBuffer *Buffer,
+                                         LLVMContext &Context,
+                                         raw_ostream *Verbose = nullptr,
+                                         bool AcceptSupportedOnly = true);
 
   /// NaClWriteBitcodeToFile - Write the specified module to the
   /// specified raw output stream, using PNaCl wire format.  For