When building Skia always have include/gpu in include path

Bug: 
Change-Id: Ia000b6af703abd81e84880ffa7449b11a61c1d89
Reviewed-on: https://chromium-review.googlesource.com/596792Reviewed-by: Brian Salomon <bsalomon@chromium.org>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Greg Daniel <egdaniel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491354}

skia/BUILD.gn

@@ -34,6 +34,7 @@ config("skia_config") {
     "//third_party/skia/include/core",
     "//third_party/skia/include/effects",
     "//third_party/skia/include/encode",
+    "//third_party/skia/include/gpu",
     "//third_party/skia/include/images",
     "//third_party/skia/include/lazy",
     "//third_party/skia/include/pathops",
@@ -63,7 +64,6 @@ config("skia_config") {
 
   if (skia_support_gpu) {
     include_dirs += [
-      "//third_party/skia/include/gpu",
       "//third_party/skia/src/gpu",
       "//third_party/skia/src/sksl",
     ]