Don't include system vulkan header when building skia files.

With this change clients will still have to have vulkan/vulkan_core.h
on their include path when compiling files that include Skia. However,
it will not be required when compiling Skia files.

Bug: skia:
Change-Id: I1cd75f4f18d3097c8a1606c3e8a51a371b01b565
Reviewed-on: https://skia-review.googlesource.com/c/179560
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index a6fcb0b..e8effe2 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -189,7 +189,6 @@
   if (skia_enable_gpu) {
     include_dirs += [ "src/gpu" ]
     if (is_skia_dev_build && skia_use_vulkan) {
-      include_dirs += [ "include/third_party/vulkan" ]
       include_dirs += [ "tools/gpu/vk" ]
     }
   }
@@ -1452,6 +1451,7 @@
       sources += [ "tools/gpu/gl/angle/GLTestContext_angle.cpp" ]
     }
 
+    public_include_dirs += [ "include/third_party/vulkan" ]
     if (skia_use_vulkan) {
       sources += [ "tools/gpu/vk/VkTestContext.cpp" ]
       sources += [ "tools/gpu/vk/VkTestUtils.cpp" ]