Add GYP target for sk_tool_utils.* component.

This declares a static library target in gyp/sk_tool_utils.gyp, so other
targets can depend directly on it instead of including the source file
in their source lists.

BUG=None
TEST=make all
R=mtklein@google.com

Author: tfarina@chromium.org

Review URL: https://codereview.chromium.org/348623006
diff --git a/gyp/tests.gypi b/gyp/tests.gypi
index f135107..9876f18 100644
--- a/gyp/tests.gypi
+++ b/gyp/tests.gypi
@@ -23,6 +23,7 @@
     'skia_lib.gyp:skia_lib',
     'tools.gyp:picture_utils',
     'tools.gyp:resources',
+    'tools.gyp:sk_tool_utils',
   ],
   'sources': [
     '../tests/Test.cpp',
@@ -197,7 +198,5 @@
 
     '../tests/TDStackNesterTest.cpp',
     '../experimental/PdfViewer/src/SkTDStackNester.h',
-
-    '../tools/sk_tool_utils.cpp',
   ],
 }