crash_dump: fork a copy of the target's address space.

Reduce the amount of time that a process remains paused by pausing its
threads, fetching their registers, and then performing unwinding on a
copy of its address space. This also works around a kernel change
that's in 4.9 that prevents ptrace from reading memory of processes
that we don't have immediate permissions to ptrace (even if we
previously ptraced them).

Bug: http://b/62112103
Bug: http://b/63989615
Test: treehugger
Change-Id: I7b9cc5dd8f54a354bc61f1bda0d2b7a8a55733c4
diff --git a/debuggerd/util.cpp b/debuggerd/util.cpp
index 0bb07ac..50c5efc 100644
--- a/debuggerd/util.cpp
+++ b/debuggerd/util.cpp
@@ -18,8 +18,12 @@
 
 #include <sys/socket.h>
 
+#include <string>
 #include <utility>
 
+#include <android-base/file.h>
+#include <android-base/stringprintf.h>
+#include <android-base/strings.h>
 #include <android-base/unique_fd.h>
 #include <cutils/sockets.h>
 #include "protocol.h"
@@ -86,3 +90,15 @@
 
   return result;
 }
+
+std::string get_process_name(pid_t pid) {
+  std::string result = "<unknown>";
+  android::base::ReadFileToString(android::base::StringPrintf("/proc/%d/cmdline", pid), &result);
+  return result;
+}
+
+std::string get_thread_name(pid_t tid) {
+  std::string result = "<unknown>";
+  android::base::ReadFileToString(android::base::StringPrintf("/proc/%d/comm", tid), &result);
+  return android::base::Trim(result);
+}