Fix cpplint runtime/explicit issues

Change-Id: I352ba0b427f1ff9b22887693952b180eae0839ba
diff --git a/compiler/dex/local_value_numbering.h b/compiler/dex/local_value_numbering.h
index f2b2291..09ed7ae 100644
--- a/compiler/dex/local_value_numbering.h
+++ b/compiler/dex/local_value_numbering.h
@@ -33,7 +33,7 @@
 
 class LocalValueNumbering {
  public:
-  LocalValueNumbering(CompilationUnit* cu) : cu_(cu) {};
+  explicit LocalValueNumbering(CompilationUnit* cu) : cu_(cu) {};
 
   static uint64_t BuildKey(uint16_t op, uint16_t operand1, uint16_t operand2, uint16_t modifier) {
     return (static_cast<uint64_t>(op) << 48 | static_cast<uint64_t>(operand1) << 32 |