Prototype for build warning as error.

BUG=

Review URL: https://codereview.chromium.org/17060004

git-svn-id: http://skia.googlecode.com/svn/trunk@9613 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/samplecode/SampleColorFilter.cpp b/samplecode/SampleColorFilter.cpp
index 126ee47..7218268 100644
--- a/samplecode/SampleColorFilter.cpp
+++ b/samplecode/SampleColorFilter.cpp
@@ -85,6 +85,7 @@
 }
 
 // No longer marked static, since it is externed in SampleUnpremul.
+SkShader* createChecker();
 SkShader* createChecker() {
     SkBitmap bm;
     bm.setConfig(SkBitmap::kARGB_8888_Config, 2, 2);