GN/Win: hook in GPU support

Just a simple oversight... this should make Ganesh work.

CQ_INCLUDE_TRYBOTS=master.client.skia.compile:Build-Win-MSVC-x86-Debug-Exceptions-Trybot,Build-Win-MSVC-x86_64-Debug-GN-Trybot,Build-Win-MSVC-x86_64-Release-GN-Trybot
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3382

Change-Id: I90353732a137d004b884cea75f1bd722ede24888
Reviewed-on: https://skia-review.googlesource.com/3382
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index d402f59..7935e74 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -363,16 +363,19 @@
                              "src/gpu/gl/GrGLDefaultInterface_none.cpp",
                            ],
                            "abspath")
+  libs = []
   if (is_android) {
     sources += [ "src/gpu/gl/android/GrGLCreateNativeInterface_android.cpp" ]
   } else if (is_linux) {
     sources += [ "src/gpu/gl/glx/GrGLCreateNativeInterface_glx.cpp" ]
   } else if (is_mac) {
     sources += [ "src/gpu/gl/mac/GrGLCreateNativeInterface_mac.cpp" ]
+  } else if (is_win) {
+    sources += [ "src/gpu/gl/win/GrGLCreateNativeInterface_win.cpp" ]
+    libs += [ "OpenGL32.lib" ]
   } else {
     sources += [ "src/gpu/gl/GrGLCreateNativeInterface_none.cpp" ]
   }
-  libs = []
 
   if (skia_use_vulkan) {
     public_defines += [ "SK_VULKAN" ]