Second wave of Win64 warning cleanup

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 97 matching lines @@
         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) {
     SkString diffName (filename);
     const char* cstring = diffName.c_str();
-    int dotOffset = strrchr(cstring, '.') - cstring;
+    size_t dotOffset = strrchr(cstring, '.') - cstring;
     diffName.remove(dotOffset, diffName.size() - dotOffset);
     diffName.append(suffix);
 
     // In case we recursed into subdirectories, replace slashes with something else
     // so the diffs will all be written into a single flat directory.
     diffName = replace_all(diffName, PATH_DIV_STR, "_");
     return diffName;
 }
 
 SkString filename_to_diff_filename(const SkString& filename) {
@@ skipping 48 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;
             }
         }
     }
 }