symbolize: don't stringify errno if we're using google::Symbolize.

base/debug_util_posix.cc

Index: base/debug_util_posix.cc
diff --git a/base/debug_util_posix.cc b/base/debug_util_posix.cc
index dfafc13bfae55a632dae35aa05971aea40082d81..7d7aca4c63687d1851e6baffd76b696805ba6cf8 100644
--- a/base/debug_util_posix.cc
+++ b/base/debug_util_posix.cc
@@ -99,9 +99,11 @@ void DemangleSymbols(std::string* text) {
 
 // Gets the backtrace as a vector of strings. If possible, resolve symbol
 // names and attach these. Otherwise just use raw addresses. Returns true
-// if any symbol name is resolved.
+// if any symbol name is resolved.  Returns false on error and *may* fill
+// in |error_message| if an error message is available.
 bool GetBacktraceStrings(void **trace, int size,
-                         std::vector<std::string>* trace_strings) {
+                         std::vector<std::string>* trace_strings,
+                         std::string* error_message) {
   bool symbolized = false;
 
 #if defined(USE_SYMBOLIZE)
@@ -130,6 +132,8 @@ bool GetBacktraceStrings(void **trace, int size,
     }
     symbolized = true;
   } else {
+    if (error_message)
+      *error_message = safe_strerror(errno);
     for (int i = 0; i < size; ++i) {
       trace_strings->push_back(base::StringPrintf("%p", trace[i]));
     }
@@ -282,7 +286,7 @@ void StackTrace::PrintBacktrace() {
 #endif
   fflush(stderr);
   std::vector<std::string> trace_strings;
-  GetBacktraceStrings(trace_, count_, &trace_strings);
+  GetBacktraceStrings(trace_, count_, &trace_strings, NULL);
   for (size_t i = 0; i < trace_strings.size(); ++i) {
     std::cerr << "\t" << trace_strings[i] << "\n";
   }
@@ -294,11 +298,14 @@ void StackTrace::OutputToStream(std::ostream* os) {
     return;
 #endif
   std::vector<std::string> trace_strings;
-  if (GetBacktraceStrings(trace_, count_, &trace_strings)) {
+  std::string error_message;
+  if (GetBacktraceStrings(trace_, count_, &trace_strings, &error_message)) {
     (*os) << "Backtrace:\n";
   } else {
-    (*os) << "Unable get symbols for backtrace (" << safe_strerror(errno)
-          << "). Dumping raw addresses in trace:\n";
+    if (!error_message.empty())
+      error_message = " (" + error_message + ")";
+    (*os) << "Unable to get symbols for backtrace" << error_message << ". "
+          << "Dumping raw addresses in trace:\n";
   }
 
   for (size_t i = 0; i < trace_strings.size(); ++i) {