Rework CFX_CountRef in terms of CFX_RetainPtr

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index ca2338f6fd5abac97b42a5cf9a3803b21ce7bb55..95507aeaa3283933178248a4202809e942dc4293 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -686,6 +686,7 @@ static_library("fxcrt") {
     "core/fxcrt/fxcrt_stream.cpp",
     "core/fxcrt/fxcrt_windows.cpp",
     "core/fxcrt/fxcrt_windows.h",
+    "core/fxcrt/include/cfx_count_ref.h",
     "core/fxcrt/include/cfx_retain_ptr.h",
     "core/fxcrt/include/fx_basic.h",
     "core/fxcrt/include/fx_coordinates.h",
@@ -1599,6 +1600,7 @@ test("pdfium_unittests") {
     "core/fpdftext/fpdf_text_int_unittest.cpp",
     "core/fxcodec/codec/fx_codec_jpx_unittest.cpp",
     "core/fxcodec/jbig2/JBig2_Image_unittest.cpp",
+    "core/fxcrt/cfx_count_ref_unittest.cpp",
     "core/fxcrt/cfx_retain_ptr_unittest.cpp",
     "core/fxcrt/fx_basic_bstring_unittest.cpp",
     "core/fxcrt/fx_basic_gcc_unittest.cpp",