Add an optional root prefix to Linux dumpers

src/client/linux/minidump_writer/linux_core_dumper.h

Index: src/client/linux/minidump_writer/linux_core_dumper.h
diff --git a/src/client/linux/minidump_writer/linux_core_dumper.h b/src/client/linux/minidump_writer/linux_core_dumper.h
index 8537896eecf4c5e4fe017fae9c4262eb734a7e37..8a7c924b61cd121cd01af2a7935ef5927e30d8a0 100644
--- a/src/client/linux/minidump_writer/linux_core_dumper.h
+++ b/src/client/linux/minidump_writer/linux_core_dumper.h
@@ -47,7 +47,9 @@ class LinuxCoreDumper : public LinuxDumper {
   // its proc files at |procfs_path|. If |procfs_path| is a copy of
   // /proc/<pid>, it should contain the following files:
   //     auxv, cmdline, environ, exe, maps, status
-  LinuxCoreDumper(pid_t pid, const char* core_path, const char* procfs_path);
+  // See LinuxDumper for the purpose of |root_prefix|.
+  LinuxCoreDumper(pid_t pid, const char* core_path, const char* procfs_path,
+                  const char* root_prefix = "");
 
   // Implements LinuxDumper::BuildProcPath().
   // Builds a proc path for a certain pid for a node (/proc/<pid>/<node>).