Change name of NativeTheme::instance() to make it clear it's web only.

ui/native_theme/native_theme_aurawin.cc

Index: ui/native_theme/native_theme_aurawin.cc
diff --git a/ui/native_theme/native_theme_aurawin.cc b/ui/native_theme/native_theme_aurawin.cc
index 1730de149dca0af66c41b9a2a568f8ba22ed8d3a..956186b535c3effc7e7333d1f883afe3c09129c2 100644
--- a/ui/native_theme/native_theme_aurawin.cc
+++ b/ui/native_theme/native_theme_aurawin.cc
@@ -34,7 +34,7 @@ bool IsScrollbarPart(NativeTheme::Part part) {
 }  // namespace
 
 // static
-NativeTheme* NativeTheme::instance() {
+NativeTheme* NativeTheme::GetInstanceForWeb() {
   return NativeThemeAuraWin::instance();
 }