Change the screenshot file format not to use colons.

chrome/browser/ui/ash/screenshot_taker.cc

Index: chrome/browser/ui/ash/screenshot_taker.cc
diff --git a/chrome/browser/ui/ash/screenshot_taker.cc b/chrome/browser/ui/ash/screenshot_taker.cc
index f11a55f0b0ef34e6f93f489df02cd87a1a302ce7..197bfe8dc2da68ac60b1f22b56e504018856bf81 100644
--- a/chrome/browser/ui/ash/screenshot_taker.cc
+++ b/chrome/browser/ui/ash/screenshot_taker.cc
@@ -59,11 +59,11 @@ FilePath GetScreenshotPath(const FilePath& base_directory,
   // for non-English locales.
   // TODO(mukai): integrate this logic somewhere time_formatting.h
   std::string file_name = base::StringPrintf(
-      "Screenshot %d-%02d-%02d ", now.year, now.month, now.day_of_month);
+      "Screenshot %d-%02d-%02d at ", now.year, now.month, now.day_of_month);
 
   if (use_24hour_clock) {
     file_name.append(base::StringPrintf(
-        "%02d:%02d:%02d", now.hour, now.minute, now.second));
+        "%02d.%02d.%02d", now.hour, now.minute, now.second));
   } else {
     int hour = now.hour;
     if (hour > 12) {
@@ -72,7 +72,7 @@ FilePath GetScreenshotPath(const FilePath& base_directory,
       hour = 12;
     }
     file_name.append(base::StringPrintf(
-        "%d:%02d:%02d ", hour, now.minute, now.second));
+        "%d.%02d.%02d ", hour, now.minute, now.second));
     file_name.append((now.hour >= 12) ? "PM" : "AM");
   }