Allow the creation of human-friendly ASTDumper to arbitrary output stream

Summary:
`ASTPrinter` allows setting the ouput to any O-Stream, but that printer creates source-code-like syntax (and is also marked with a `FIXME`). The nice, colourful, mostly human-readable `ASTDumper` only works on the standard output, which is not feasible in case a user wants to see the AST of a file through a code navigation/comprehension tool.

This small addition of an overload solves generating a nice colourful AST block for the users of a tool I'm working on, [[ http://github.com/Ericsson/CodeCompass | CodeCompass ]], as opposed to having to duplicate the behaviour of definitions that only exist in the anonymous namespace of implementation TUs related to this module.

Reviewers: alexfh, klimek, rsmith

Reviewed By: alexfh

Subscribers: rnkovacs, dkrupp, gsd, xazax.hun, cfe-commits, #clang

Tags: #clang

Patch by Whisperity!

Differential Revision: https://reviews.llvm.org/D45096

llvm-svn: 329391
diff --git a/clang/lib/Frontend/FrontendActions.cpp b/clang/lib/Frontend/FrontendActions.cpp
index 1eff566..8cb6a04 100644
--- a/clang/lib/Frontend/FrontendActions.cpp
+++ b/clang/lib/Frontend/FrontendActions.cpp
@@ -74,7 +74,8 @@
 
 std::unique_ptr<ASTConsumer>
 ASTDumpAction::CreateASTConsumer(CompilerInstance &CI, StringRef InFile) {
-  return CreateASTDumper(CI.getFrontendOpts().ASTDumpFilter,
+  return CreateASTDumper(nullptr /*Dump to stdout.*/,
+                         CI.getFrontendOpts().ASTDumpFilter,
                          CI.getFrontendOpts().ASTDumpDecls,
                          CI.getFrontendOpts().ASTDumpAll,
                          CI.getFrontendOpts().ASTDumpLookups);