Start cleaning up 64bit Win warnings

tools/skdiff_utils.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "skdiff.h"
 #include "skdiff_utils.h"
 #include "SkBitmap.h"
 #include "SkData.h"
@@ skipping 84 matching lines @@
 /// of oldSubstring with newSubstring.
 ///
 /// TODO: If we like this, we should move it into the core SkString implementation,
 /// adding more checks and ample test cases, and paying more attention to efficiency.
 static SkString replace_all(const SkString &input,
                             const char oldSubstring[], const char newSubstring[]) {
     SkString output;
     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);
         first_char = match_char + oldSubstringLen;
     }
     output.append(first_char);
     return output;
 }
 
 static SkString filename_to_derived_filename(const SkString& filename, const char *suffix) {
@@ skipping 61 matching lines @@
                 drp->fDifference.fStatus = DiffResource::kDoesNotExist_Status;
             }
             if (write_bitmap(drp->fWhite.fFullPath, drp->fWhite.fBitmap)) {
                 drp->fWhite.fStatus = DiffResource::kExists_Status;
             } else {
                 drp->fWhite.fStatus = DiffResource::kDoesNotExist_Status;
             }
         }
     }
 }