debuggerd: fix several bugs caused by fork/setuid change.

Previously, we weren't PTRACE_ATTACHing to all of the threads of a
process, and we were also trying to do it after forking and dropping
privileges. This patch ensures that all ptrace attaching/detaching
happens in one place, before forking/exiting respectively.

Bug: http://b/26443860
Bug: http://b/26436605
Bug: http://b/26436486
Change-Id: Id94e0c1d9d56c051d0dd281d895aaa3285079198
diff --git a/debuggerd/backtrace.h b/debuggerd/backtrace.h
index da14cd4..98c433b 100644
--- a/debuggerd/backtrace.h
+++ b/debuggerd/backtrace.h
@@ -19,14 +19,17 @@
 
 #include <sys/types.h>
 
+#include <set>
+
 #include "utility.h"
 
 class Backtrace;
+class BacktraceMap;
 
 // Dumps a backtrace using a format similar to what Dalvik uses so that the result
 // can be intermixed in a bug report.
-void dump_backtrace(int fd, int amfd, pid_t pid, pid_t tid, bool* detach_failed,
-                    int* total_sleep_time_usec);
+void dump_backtrace(int fd, int amfd, BacktraceMap* map, pid_t pid, pid_t tid,
+                    const std::set<pid_t>& siblings);
 
 /* Dumps the backtrace in the backtrace data structure to the log. */
 void dump_backtrace_to_log(Backtrace* backtrace, log_t* log, const char* prefix);