Add include paths in gputest.gyp for use by additional gpu tests.

BUG=skia:

Review URL: https://codereview.chromium.org/1290553005
diff --git a/gyp/gpu.gyp b/gyp/gpu.gyp
index bfd9d38..51e7e32 100644
--- a/gyp/gpu.gyp
+++ b/gyp/gpu.gyp
@@ -112,7 +112,10 @@
         [ 'skia_gpu_extra_dependency_path', {
           'dependencies' : [
               '<(skia_gpu_extra_dependency_path):*',
-          ]
+          ],
+          'export_dependent_settings': [
+            '<(skia_gpu_extra_dependency_path):*',
+          ],
         }],
         [ 'skia_chrome_utils', {
           'sources': [