Clean up singleton implementation

Move the singleton instances into their namespaces, and use
get()/getInstance() for uniform accesses.

Review-Url: https://codereview.chromium.org/2154843002
diff --git a/BUILD.gn b/BUILD.gn
index 7758f20..5bd104d 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -800,6 +800,8 @@
       "fpdfsdk/javascript/JS_EventHandler.h",
       "fpdfsdk/javascript/JS_GlobalData.cpp",
       "fpdfsdk/javascript/JS_GlobalData.h",
+      "fpdfsdk/javascript/JS_KeyValue.cpp",
+      "fpdfsdk/javascript/JS_KeyValue.h",
       "fpdfsdk/javascript/JS_Object.cpp",
       "fpdfsdk/javascript/JS_Object.h",
       "fpdfsdk/javascript/JS_Value.cpp",
@@ -1095,6 +1097,8 @@
       "xfa/fwl/lightwidget/cfwl_widget.h",
       "xfa/fwl/lightwidget/cfwl_widgetproperties.cpp",
       "xfa/fwl/lightwidget/cfwl_widgetproperties.h",
+      "xfa/fwl/theme/cfwl_arrowdata.cpp",
+      "xfa/fwl/theme/cfwl_arrowdata.h",
       "xfa/fwl/theme/cfwl_barcodetp.cpp",
       "xfa/fwl/theme/cfwl_barcodetp.h",
       "xfa/fwl/theme/cfwl_carettp.cpp",