init prevLevel to avoid warning

git-svn-id: http://skia.googlecode.com/svn/trunk@10166 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tests/MipMapTest.cpp b/tests/MipMapTest.cpp
index c305532..9e1d463 100644
--- a/tests/MipMapTest.cpp
+++ b/tests/MipMapTest.cpp
@@ -31,7 +31,7 @@
         REPORTER_ASSERT(reporter, !mm->extractLevel(SK_Scalar1, NULL));
         REPORTER_ASSERT(reporter, !mm->extractLevel(SK_Scalar1 * 2, NULL));
         
-        SkMipMap::Level prevLevel;
+        SkMipMap::Level prevLevel = { 0 };  // make warnings happy
         prevLevel.fPixels = NULL;   // sentinel
 
         SkScalar scale = SK_Scalar1;