Start cleaning up 64bit Win warnings

https://codereview.chromium.org/27192003/



git-svn-id: http://skia.googlecode.com/svn/trunk@11764 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/skdiff_utils.cpp b/tools/skdiff_utils.cpp
index 0eb405a..1f5289b 100644
--- a/tools/skdiff_utils.cpp
+++ b/tools/skdiff_utils.cpp
@@ -102,7 +102,7 @@
     const char *input_cstr = input.c_str();
     const char *first_char = input_cstr;
     const char *match_char;
-    int oldSubstringLen = strlen(oldSubstring);
+    size_t oldSubstringLen = strlen(oldSubstring);
     while (NULL != (match_char = strstr(first_char, oldSubstring))) {
         output.append(first_char, (match_char - first_char));
         output.append(newSubstring);