Put in place the ARM64 instruction simplification framework.

This commit introduces and runs the empty InstructionSimplifierArm64
pass. Further commits will introduce arm64-specific transformations in
that pass.

Change-Id: I458f8a2b15470297b87fc1f7ff85bd52155d93ef
diff --git a/compiler/optimizing/optimizing_compiler_stats.h b/compiler/optimizing/optimizing_compiler_stats.h
index 53d052b..da5cb57 100644
--- a/compiler/optimizing/optimizing_compiler_stats.h
+++ b/compiler/optimizing/optimizing_compiler_stats.h
@@ -32,6 +32,7 @@
   kCompiledQuick,
   kInlinedInvoke,
   kInstructionSimplifications,
+  kInstructionSimplificationsArch,
   kNotCompiledBranchOutsideMethodCode,
   kNotCompiledCannotBuildSSA,
   kNotCompiledCantAccesType,
@@ -101,6 +102,7 @@
       case kCompiledQuick : return "kCompiledQuick";
       case kInlinedInvoke : return "kInlinedInvoke";
       case kInstructionSimplifications: return "kInstructionSimplifications";
+      case kInstructionSimplificationsArch: return "kInstructionSimplificationsArch";
       case kNotCompiledBranchOutsideMethodCode: return "kNotCompiledBranchOutsideMethodCode";
       case kNotCompiledCannotBuildSSA : return "kNotCompiledCannotBuildSSA";
       case kNotCompiledCantAccesType : return "kNotCompiledCantAccesType";