crash-reporter: Change layout for the container directory of procfs files.

This CL modifies UserCollector to copy procfs files of a crashed process
into /tmp/crash_reporter/<pid> instead of /tmp/crash_reporter.<pid>.
The new directory layout makes it easier for autotest to archive
leftover files under /tmp/crash_reporter due to core2md failures.

BUG=chromium-os:24646
TEST=Tested the following:
1. Build crash-reporter and run unit tests.
2. Run the following autotest tests on a Cr48:
   - logging_CrashSender
   - logging_UserCrash

Change-Id: I435374eabc1574216881318ddacdfa9d1648c875
Reviewed-on: https://gerrit.chromium.org/gerrit/13697
Commit-Ready: Ben Chan <benchan@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
diff --git a/crash_reporter/user_collector.cc b/crash_reporter/user_collector.cc
index f53a61b..01af4eb 100644
--- a/crash_reporter/user_collector.cc
+++ b/crash_reporter/user_collector.cc
@@ -366,10 +366,9 @@
     return false;
   }
 
-  // Directory like /tmp/crash_reporter.1234 which contains the
+  // Directory like /tmp/crash_reporter/1234 which contains the
   // procfs entries and other temporary files used during conversion.
-  FilePath container_dir = FilePath("/tmp").Append(
-      StringPrintf("crash_reporter.%d", pid));
+  FilePath container_dir(StringPrintf("/tmp/crash_reporter/%d", pid));
   // Delete a pre-existing directory from crash reporter that may have
   // been left around for diagnostics from a failed conversion attempt.
   // If we don't, existing files can cause forking to fail.