Fix cpplint runtime/explicit issues

Change-Id: I352ba0b427f1ff9b22887693952b180eae0839ba
diff --git a/runtime/oat/utils/x86/assembler_x86.h b/runtime/oat/utils/x86/assembler_x86.h
index 390f7aa..3f40a54 100644
--- a/runtime/oat/utils/x86/assembler_x86.h
+++ b/runtime/oat/utils/x86/assembler_x86.h
@@ -643,7 +643,7 @@
 // Slowpath entered when Thread::Current()->_exception is non-null
 class X86ExceptionSlowPath : public SlowPath {
  public:
-  X86ExceptionSlowPath(size_t stack_adjust) : stack_adjust_(stack_adjust) {}
+  explicit X86ExceptionSlowPath(size_t stack_adjust) : stack_adjust_(stack_adjust) {}
   virtual void Emit(Assembler *sp_asm);
  private:
   const size_t stack_adjust_;