Refactor some X86 Stackwalker bits into parent classes

src/processor/stackwalker_x86.h

Index: src/processor/stackwalker_x86.h
===================================================================
--- a/src/processor/stackwalker_x86.h
+++ b/src/processor/stackwalker_x86.h
@@ -91,29 +91,16 @@ class StackwalkerX86 : public Stackwalke
 
   // Assuming a traditional frame layout --- where the caller's %ebp
   // has been pushed just after the return address and the callee's
   // %ebp points to the saved %ebp --- construct the frame that called
   // frames.back(). The caller takes ownership of the returned frame.
   // Return NULL on failure.
   StackFrameX86 *GetCallerByEBPAtBase(const vector<StackFrame*> &frames);
 
-  // Scan the stack starting at location_start, looking for an address
-  // that looks like a valid instruction pointer. Addresses must
-  // 1) be contained in the current stack memory
-  // 2) pass the checks in Stackwalker::InstructionAddressSeemsValid
-  //
-  // Returns true if a valid-looking instruction pointer was found.
-  // When returning true, sets location_found to the address at which
-  // the value was found, and eip_found to the value contained at that
-  // location in memory.
-  bool ScanForReturnAddress(u_int32_t location_start,
-                            u_int32_t *location_found,
-                            u_int32_t *eip_found);
-
   // Stores the CPU context corresponding to the innermost stack frame to
   // be returned by GetContextFrame.
   const MDRawContextX86 *context_;
 
   // Our register map, for cfi_walker_.
   static const CFIWalker::RegisterSet cfi_register_map_[];
 
   // Our CFI frame walker.