Rename an argument named "register" to "reg".

This silences a warning in newer versions of clang that complains
about "register" being a deprecated keyword.

Bug: chromium:780692
Reviewed-on: https://chromium-review.googlesource.com/750362
Reviewed-by: Mark Mentovai <mark@chromium.org>

(cherry picked from commit 2d85d492aeb9eeb889885e84b3666d64407f2920)

Bug: http://b/111067277
Test: builds
Exempt-From-Owner-Approval: janitorial
Change-Id: I01d310dc397433a472e272f30d65813138f02cd5
diff --git a/src/common/dwarf/dwarf2reader.cc b/src/common/dwarf/dwarf2reader.cc
index f2f3d58..a1e610d 100644
--- a/src/common/dwarf/dwarf2reader.cc
+++ b/src/common/dwarf/dwarf2reader.cc
@@ -870,12 +870,12 @@
  public:
   virtual ~Rule() { }
 
-  // Tell HANDLER that, at ADDRESS in the program, REGISTER can be
-  // recovered using this rule. If REGISTER is kCFARegister, then this rule
-  // describes how to compute the canonical frame address. Return what the
-  // HANDLER member function returned.
+  // Tell HANDLER that, at ADDRESS in the program, REG can be recovered using
+  // this rule. If REG is kCFARegister, then this rule describes how to compute
+  // the canonical frame address. Return what the HANDLER member function
+  // returned.
   virtual bool Handle(Handler *handler,
-                      uint64 address, int register) const = 0;
+                      uint64 address, int reg) const = 0;
 
   // Equality on rules. We use these to decide which rules we need
   // to report after a DW_CFA_restore_state instruction.