Add missing 'explicit's on single-argument constructors.

Change-Id: I1494df6e74ec16238971fb4346ba184eb61c37ab
diff --git a/src/dex_instruction.h b/src/dex_instruction.h
index e08a1f7..2c1a397 100644
--- a/src/dex_instruction.h
+++ b/src/dex_instruction.h
@@ -99,7 +99,7 @@
     uint32_t arg_[5];         /* vC/D/E/F/G in invoke or filled-new-array */
     Code     opcode_;
 
-    DecodedInstruction(const Instruction* inst) {
+    explicit DecodedInstruction(const Instruction* inst) {
       inst->Decode(vA_, vB_, vB_wide_, vC_, arg_);
       opcode_ = inst->Opcode();
     }