use most innocuous characters possible within skimage output filenames

tools/skimage_main.cpp

Index: tools/skimage_main.cpp
diff --git a/tools/skimage_main.cpp b/tools/skimage_main.cpp
index e5610ea569d16a43054e6194968da892723e4750..3740f0fa079758c2a7739a749732cebafc27fc44 100644
--- a/tools/skimage_main.cpp
+++ b/tools/skimage_main.cpp
@@ -595,7 +595,7 @@ static void decodeFileAndWrite(const char srcPath[], const SkString* writePath)
                 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());