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/bench.gyp b/gyp/bench.gyp
index 1c19437..9089bf8 100644
--- a/gyp/bench.gyp
+++ b/gyp/bench.gyp
@@ -15,6 +15,7 @@
         'skia_lib.gyp:skia_lib',
         'tools.gyp:crash_handler',
         'tools.gyp:resources',
+        'tools.gyp:sk_tool_utils',
         'tools.gyp:timer',
       ],
       'sources': [
@@ -24,7 +25,6 @@
         '../bench/GMBench.h',
         '../bench/ResultsWriter.cpp',
         '../bench/benchmain.cpp',
-        '../tools/sk_tool_utils.cpp',
       ],
       'conditions': [
         ['skia_gpu == 1',