fix warning from scalar --> int32 conversion

BUG=

Review URL: https://codereview.appspot.com/7065050

git-svn-id: http://skia.googlecode.com/svn/trunk@7061 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/pipe/utils/SamplePipeControllers.cpp b/src/pipe/utils/SamplePipeControllers.cpp
index 59f612b..98fdff3 100644
--- a/src/pipe/utils/SamplePipeControllers.cpp
+++ b/src/pipe/utils/SamplePipeControllers.cpp
@@ -51,7 +51,7 @@
         rect.setLTRB(0, top, bitmap.width(), bottom);
         top = bottom;
 
-        bool extracted = bitmap.extractSubset(&fBitmaps[i], rect);
+        SkDEBUGCODE(bool extracted = )bitmap.extractSubset(&fBitmaps[i], rect);
         SkASSERT(extracted);
         SkDevice* device = new SkDevice(fBitmaps[i]);
         SkCanvas* canvas = new SkCanvas(device);