Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: Ic7e236a7f58c4021a3f8fb4536a6457d262fe62e
diff --git a/runtime/quick_exception_handler.cc b/runtime/quick_exception_handler.cc
index a785ecb..e32f86b 100644
--- a/runtime/quick_exception_handler.cc
+++ b/runtime/quick_exception_handler.cc
@@ -611,7 +611,7 @@
 // Prints out methods with their type of frame.
 class DumpFramesWithTypeStackVisitor FINAL : public StackVisitor {
  public:
-  DumpFramesWithTypeStackVisitor(Thread* self, bool show_details = false)
+  explicit DumpFramesWithTypeStackVisitor(Thread* self, bool show_details = false)
       SHARED_REQUIRES(Locks::mutator_lock_)
       : StackVisitor(self, nullptr, StackVisitor::StackWalkKind::kIncludeInlinedFrames),
         show_details_(show_details) {}