use most innocuous characters possible within skimage output filenames

tools/skimage_main.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm_expectations.h"
 #include "SkBitmap.h"
 #include "SkColorPriv.h"
@@ skipping 577 matching lines @@
         // Build the tile index for decoding subsets. If the image is 1x1, skip subset
         // decoding since there are no smaller subsets.
         if (codec->buildTileIndex(&stream, &width, &height) && width > 1 && height > 1) {
             SkASSERT(bitmap.width() == width && bitmap.height() == height);
             // Call decodeSubset multiple times:
             SkRandom rand(0);
             for (int i = 0; i < 5; i++) {
                 SkBitmap bitmapFromDecodeSubset;
                 // FIXME: Come up with a more representative set of rectangles.
                 SkIRect rect = generate_random_rect(&rand, width, height);
-                SkString subsetDim = SkStringPrintf("[%d,%d,%d,%d]", rect.fLeft, rect.fTop,
+                SkString subsetDim = SkStringPrintf("%d_%d_%d_%d", rect.fLeft, rect.fTop,

[epoger, 2014/06/02 21:12:29]

Sigh.  My previous attempt (using parentheses) yielded different errors, at
http://108.170.220.120:10117/builders/Test-ChromeOS-Link-HD4000-x86_64-Releas...

This should result in filenames like this:
gs://chromium-skia-gm/skimage/output/images/bitmap-64bitMD5/webp-test-webp-123_263_587_394/16263897892077508819.png

It's not the best thing ever, but I'm looking for something that won't cause
problems for gsutil OR Linux/Mac shell command lines OR Windows command lines.

Any better ideas?

                                                     rect.fRight, rect.fBottom);
                 if (codec->decodeSubset(&bitmapFromDecodeSubset, rect, gPrefConfig)) {
                     SkString subsetName = SkStringPrintf("%s-%s", filename, subsetDim.c_str());
                     skiagm::BitmapAndDigest subsetBitmapAndDigest(bitmapFromDecodeSubset);
                     if (compare_to_expectations_if_necessary(subsetBitmapAndDigest.fDigest,
                                                              subsetName.c_str(),
                                                              &gFailedSubsetDecodes,
                                                              &gMissingSubsetExpectations,
                                                              &gKnownSubsetFailures)) {
                         gSuccessfulSubsetDecodes.push_back().printf("Decoded subset %s from %s",
@@ skipping 225 matching lines @@
     print_strings("Known failures", gKnownFailures);
 
     return failed ? -1 : 0;
 }
 
 #if !defined SK_BUILD_FOR_IOS
 int main(int argc, char * const argv[]) {
     return tool_main(argc, (char**) argv);
 }
 #endif