Create new target to hold gpu test code, enable direct testing of GrEffects in GM.

gyp/SampleApp.gyp

Index: gyp/SampleApp.gyp
diff --git a/gyp/SampleApp.gyp b/gyp/SampleApp.gyp
index 07516515a6b5b8308ca4abd4fb684bc9c84ed46f..aa6cbe08d8d9457b4cfc7cba64f9d68c16ee406c 100644
--- a/gyp/SampleApp.gyp
+++ b/gyp/SampleApp.gyp
@@ -300,8 +300,8 @@
           ],
         }],
         [ 'skia_gpu == 1', {
-          'include_dirs': [
-            '../src/gpu', # To pull gl/GrGLUtil.h
+          'dependencies': [
+            'gputest.gyp:skgputest',
           ],
         }],
         [ 'skia_os == "nacl"', {