Add string art GM and sample.

BUG=279014
R=robertphillips@google.com

Review URL: https://codereview.chromium.org/23609037

git-svn-id: http://skia.googlecode.com/svn/trunk@11383 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/SampleApp.gyp b/gyp/SampleApp.gyp
index f4a1d78..7b8b4bd 100644
--- a/gyp/SampleApp.gyp
+++ b/gyp/SampleApp.gyp
@@ -103,6 +103,7 @@
         '../samplecode/SampleShaderText.cpp',
         '../samplecode/SampleSkLayer.cpp',
         '../samplecode/SampleSlides.cpp',
+        '../samplecode/SampleStringArt.cpp',
         '../samplecode/SampleStrokePath.cpp',
         '../samplecode/SampleTests.cpp',
         '../samplecode/SampleText.cpp',