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/Tooling/CompilationDatabaseTest.cpp b/unittests/Tooling/CompilationDatabaseTest.cpp
index 591d48d..560b931 100644
--- a/unittests/Tooling/CompilationDatabaseTest.cpp
+++ b/unittests/Tooling/CompilationDatabaseTest.cpp
@@ -11,7 +11,7 @@
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclGroup.h"
 #include "clang/Frontend/FrontendAction.h"
-#include "clang/Tooling/CompilationDatabase.h"
+#include "clang/Tooling/JSONCompilationDatabase.h"
 #include "clang/Tooling/Tooling.h"
 #include "gtest/gtest.h"