Move last of platform dependent init from //ui/gl to //ui/gl/init.

ui/gl/BUILD.gn

Index: ui/gl/BUILD.gn
diff --git a/ui/gl/BUILD.gn b/ui/gl/BUILD.gn
index 6a23f5e304ec13a36df04f50201dae767dc4a120..d2a6c3c3c37ec4bf38198dba62cddeed2647727d 100644
--- a/ui/gl/BUILD.gn
+++ b/ui/gl/BUILD.gn
@@ -87,9 +87,6 @@ component("gl") {
     "gl_image_stub.h",
     "gl_implementation.cc",
     "gl_implementation.h",
-    "gl_implementation_android.cc",
-    "gl_implementation_mac.cc",
-    "gl_implementation_win.cc",
     "gl_osmesa_api_implementation.cc",
     "gl_osmesa_api_implementation.h",
     "gl_share_group.cc",
@@ -175,7 +172,6 @@ component("gl") {
   }
   if (use_x11) {
     sources += [
-      "gl_implementation_x11.cc",
       "gl_surface_egl_x11.cc",
       "gl_surface_egl_x11.h",
       "gl_surface_osmesa_x11.cc",
@@ -187,9 +183,6 @@ component("gl") {
       "//third_party/angle:libGLESv2",
     ]
   }
-  if (use_ozone) {
-    sources += [ "gl_implementation_ozone.cc" ]
-  }
   if (use_glx) {
     sources += [
       "gl_bindings_autogen_glx.cc",