Drive-by: Update `ui/gfx/` components

This CL is intended to be trivial.

This CL updates the component build pattern (see
`docs/component_build.md`) under `ui/gfx/`. All `GFX_EXPORT`s are now
`COMPONENT_EXPORT()`s in some form or another, and the GN recipes are
reworked slightly to use a shared config (to express that they are the
same component).

This CL was originally whipped up to investigate a compile failure in
https://crrev.com/c/5997296 (it turns out to be unrelated). Let it stand
as a horrifying demonstration of sunk cost.

Change-Id: I0d3a8ec703dfc1f6e32d46893b39128476ffd76c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6002456
Commit-Queue: Kalvin Lee <[email protected]>
Reviewed-by: Xiyuan Xia <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1380936}
diff --git a/ui/gfx/scrollbar_size.h b/ui/gfx/scrollbar_size.h
index 7f9cf39..a2f3c9e 100644
--- a/ui/gfx/scrollbar_size.h
+++ b/ui/gfx/scrollbar_size.h
@@ -5,14 +5,14 @@
 #ifndef UI_GFX_SCROLLBAR_SIZE_H_
 #define UI_GFX_SCROLLBAR_SIZE_H_
 
-#include "ui/gfx/gfx_export.h"
+#include "base/component_export.h"
 
 namespace gfx {
 
 // This should return the thickness, in pixels, of a scrollbar in web content.
 // This needs to match the values in WebCore's
 // ScrollbarThemeChromiumXXX.cpp::scrollbarThickness().
-GFX_EXPORT int scrollbar_size();
+COMPONENT_EXPORT(GFX) int scrollbar_size();
 
 }  // namespace gfx