Set USE(NEW_THEME) in config.h instead of a gyp file

Source/core/rendering/RenderTheme.h

Index: Source/core/rendering/RenderTheme.h
diff --git a/Source/core/rendering/RenderTheme.h b/Source/core/rendering/RenderTheme.h
index 057b53f3168a95bf1b994ad57f9a46c9ee7ecd6a..945bda0a0fa63386327be0dde57ac13d1c9172c4 100644
--- a/Source/core/rendering/RenderTheme.h
+++ b/Source/core/rendering/RenderTheme.h
@@ -23,6 +23,10 @@
 #ifndef RenderTheme_h
 #define RenderTheme_h
 
+#if OS(DARWIN)
+#define WTF_USE_NEW_THEME 1
+#endif

[abarth-chromium, 2013/08/12 19:43:21]

This should got in Platform.h rather than here.  We assume that USE macros a
visible globally in the project.

[lgombos, 2013/08/13 14:52:45]

It seems to me that from the ~20 USE() guards currently in Blink, most of the
guards are only used under core/ (layers on top of wtf/) and many are already
set/scoped so that they are not visible under wtf/ (WEBAUDIO_XX,
NATIVE_FULLSCREEN_VIDEO, CONCATENATED_IMPULSE_RESPONSES, etc.).

The only macro I've found that is used both under wtf/ and core/ is USE(CF), the
rest seems to be only used either under wtf/ or layers above wtf/.

We also seem to be inconsistent abut whether these macros are set in .h files or
in .gyp* files. Many are set in core/features.gypi and many in Platform.h. My
understanding was that we should aim to eliminate Platform.h in the hope of
gaining on build times.
  
I see value in scoping these macros to be either just for wtf/ or for layers
above wtf (and perhaps revisit the one/few macros that are used in both layers).

Thoughts ? 

+
 #include "core/platform/ScrollTypes.h"
 #if USE(NEW_THEME)
 #include "core/platform/Theme.h"