Add an optional root prefix to Linux dumpers

src/client/linux/minidump_writer/linux_dumper.h

Index: src/client/linux/minidump_writer/linux_dumper.h
diff --git a/src/client/linux/minidump_writer/linux_dumper.h b/src/client/linux/minidump_writer/linux_dumper.h
index 6a3a100f32376e125490a64376c7318a76c4486f..f7fe1dd9dfa39ca6c9b9cd32b994dba9ac574f5c 100644
--- a/src/client/linux/minidump_writer/linux_dumper.h
+++ b/src/client/linux/minidump_writer/linux_dumper.h
@@ -72,7 +72,9 @@ const char kLinuxGateLibraryName[] = "linux-gate.so";
 
 class LinuxDumper {
  public:
-  explicit LinuxDumper(pid_t pid);
+  // The |root_prefix| is prepended to mapping paths before opening them, which
+  // is useful if the crash originates from a chroot.
+  explicit LinuxDumper(pid_t pid, const char* root_prefix = "");
 
   virtual ~LinuxDumper();
 
@@ -140,16 +142,21 @@ class LinuxDumper {
   pid_t crash_thread() const { return crash_thread_; }
   void set_crash_thread(pid_t crash_thread) { crash_thread_ = crash_thread; }
 
+  // Concatenates the |root_prefix_| and |mapping| path. Writes into |path| and
+  // returns true unless the string is too long.
+  bool GetMappingAbsolutePath(const MappingInfo& mapping,
+                              char path[PATH_MAX]) const;
+
   // Extracts the effective path and file name of from |mapping|. In most cases
   // the effective name/path are just the mapping's path and basename. In some
   // other cases, however, a library can be mapped from an archive (e.g., when
   // loading .so libs from an apk on Android) and this method is able to
   // reconstruct the original file name.
-  static void GetMappingEffectiveNameAndPath(const MappingInfo& mapping,
-                                             char* file_path,
-                                             size_t file_path_size,
-                                             char* file_name,
-                                             size_t file_name_size);
+  void GetMappingEffectiveNameAndPath(const MappingInfo& mapping,
+                                      char* file_path,
+                                      size_t file_path_size,
+                                      char* file_name,
+                                      size_t file_name_size);
 
  protected:
   bool ReadAuxv();
@@ -172,6 +179,9 @@ class LinuxDumper {
    // ID of the crashed process.
   const pid_t pid_;
 
+  // Path of the root directory to which mapping paths are relative.
+  const char* const root_prefix_;
+
   // Virtual address at which the process crashed.
   uintptr_t crash_address_;