Fix build (warning).

BUG=

Review URL: https://codereview.chromium.org/14789014

git-svn-id: http://skia.googlecode.com/svn/trunk@8998 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/skimage_main.cpp b/tools/skimage_main.cpp
index 688d3a2..abce518 100644
--- a/tools/skimage_main.cpp
+++ b/tools/skimage_main.cpp
@@ -206,7 +206,8 @@
                         SkString suffix = SkStringPrintf("_%s.png", subsetDim.c_str());
                         SkString outPath;
                         make_outname(&outPath, writePath->c_str(), srcPath, suffix.c_str());
-                        bool success = write_bitmap(outPath.c_str(), &bitmapFromDecodeSubset);
+                        SkDEBUGCODE(bool success =)
+                        write_bitmap(outPath.c_str(), &bitmapFromDecodeSubset);
                         SkASSERT(success);
                         gSuccessfulSubsetDecodes.push_back().printf("\twrote %s", outPath.c_str());
                         // Also use extractSubset from the original for visual comparison.