Use general instruction/stack pointer convenience method instead of manually

src/google_breakpad/processor/dump_context.h

Index: src/google_breakpad/processor/dump_context.h
===================================================================
--- src/google_breakpad/processor/dump_context.h	(revision 1466)
+++ src/google_breakpad/processor/dump_context.h	(working copy)
@@ -67,6 +67,10 @@
   // MDRawContext, since it varies per-CPU architecture.
   bool GetInstructionPointer(uint64_t* ip) const;
 
+  // Similar to the GetInstructionPointer method, this method gets the stack
+  // pointer for all CPU architectures.
+  bool GetStackPointer(uint64_t* sp) const;
+
   // Print a human-readable representation of the object to stdout.
   void Print();