Add StackTrace::ToString().

base/debug/stack_trace.h

Index: base/debug/stack_trace.h
diff --git a/base/debug/stack_trace.h b/base/debug/stack_trace.h
index a524616c8c72acd0306950a40c1d3b76af4a1aed..65421b232b31bd045dfc72d4bec49a6e3b856928 100644
--- a/base/debug/stack_trace.h
+++ b/base/debug/stack_trace.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include <iosfwd>
+#include <string>
 
 #include "base/base_export.h"
 #include "build/build_config.h"
@@ -52,6 +53,9 @@ class BASE_EXPORT StackTrace {
   // Resolves backtrace to symbols and write to stream.
   void OutputToStream(std::ostream* os) const;
 
+  // Resolves backtrace to symbols and returns as string.
+  std::string ToString() const;
+
  private:
   // From http://msdn.microsoft.com/en-us/library/bb204633.aspx,
   // the sum of FramesToSkip and FramesToCapture must be less than 63,