Provide DIA implementation of DebugInfoPDB.

This implements DebugInfoPDB when the DIA SDK is present on the system.
Specifically, this means that the following conditions are met:
  1) You are building on Windows.
  2) You are building with MSVC.
  3) Visual Studio did not corrupt the installation of DIA due to a
     known issue with side-by-side installations of VS2012 and VS2013.
If all of these conditions are true, you will be able to pass a value
of PDB_Reader::DIA to PDB::createPdbReader().

There are no tests for this yet, as any test will be in the form of a
lit test which tests the llvm-pdbdump.exe, which still needs to be
rewritten in terms of this library.

llvm-svn: 228747
diff --git a/llvm/lib/DebugInfo/PDB/DIA/DIAEnumDebugStreams.cpp b/llvm/lib/DebugInfo/PDB/DIA/DIAEnumDebugStreams.cpp
new file mode 100644
index 0000000..d6e9f2a
--- /dev/null
+++ b/llvm/lib/DebugInfo/PDB/DIA/DIAEnumDebugStreams.cpp
@@ -0,0 +1,53 @@
+//==- DIAEnumDebugStreams.cpp - DIA Debug Stream Enumerator impl -*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/DebugInfo/PDB/PDBSymbol.h"
+#include "llvm/DebugInfo/PDB/DIA/DIAEnumDebugStreams.h"
+#include "llvm/DebugInfo/PDB/DIA/DIADataStream.h"
+
+using namespace llvm;
+
+DIAEnumDebugStreams::DIAEnumDebugStreams(
+    CComPtr<IDiaEnumDebugStreams> DiaEnumerator)
+    : Enumerator(DiaEnumerator) {}
+
+uint32_t DIAEnumDebugStreams::getChildCount() const {
+  LONG Count = 0;
+  return (S_OK == Enumerator->get_Count(&Count)) ? Count : 0;
+}
+
+std::unique_ptr<IPDBDataStream>
+DIAEnumDebugStreams::getChildAtIndex(uint32_t Index) const {
+  CComPtr<IDiaEnumDebugStreamData> Item;
+  VARIANT VarIndex;
+  VarIndex.vt = VT_I4;
+  VarIndex.lVal = Index;
+  if (S_OK != Enumerator->Item(VarIndex, &Item))
+    return nullptr;
+
+  return std::unique_ptr<IPDBDataStream>(new DIADataStream(Item));
+}
+
+std::unique_ptr<IPDBDataStream> DIAEnumDebugStreams::getNext() {
+  CComPtr<IDiaEnumDebugStreamData> Item;
+  ULONG NumFetched = 0;
+  if (S_OK != Enumerator->Next(1, &Item, &NumFetched))
+    return nullptr;
+
+  return std::unique_ptr<IPDBDataStream>(new DIADataStream(Item));
+}
+
+void DIAEnumDebugStreams::reset() { Enumerator->Reset(); }
+
+DIAEnumDebugStreams *DIAEnumDebugStreams::clone() const {
+  CComPtr<IDiaEnumDebugStreams> EnumeratorClone;
+  if (S_OK != Enumerator->Clone(&EnumeratorClone))
+    return nullptr;
+  return new DIAEnumDebugStreams(EnumeratorClone);
+}