Use LLVM's plugin registry to enable registering new compilation
databases. Move JSONCompilationDatabase.h to its own files and
register it as plugin.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162541 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/AST/DeclPrinterTest.cpp b/unittests/AST/DeclPrinterTest.cpp
index 758b34c..332018e 100644
--- a/unittests/AST/DeclPrinterTest.cpp
+++ b/unittests/AST/DeclPrinterTest.cpp
@@ -22,6 +22,7 @@
 #include "clang/AST/ASTContext.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/Tooling/Tooling.h"
+#include "llvm/ADT/SmallString.h"
 #include "gtest/gtest.h"
 
 using namespace clang;
@@ -1237,4 +1238,3 @@
     "Z<sizeof...(T)> A"));
     // Should be: with semicolon, without extra space in "> >"
 }
-