Fix google-explicit-constructor warnings.

* Add explicit keyword to conversion constructors.
Bug: 28341362
Test: build with WITH_TIDY=1

Change-Id: I7422d703de17c4266d2a022990d0e1df40f48226
diff --git a/tools/split-select/SplitSelector.h b/tools/split-select/SplitSelector.h
index 193fda7..120354f 100644
--- a/tools/split-select/SplitSelector.h
+++ b/tools/split-select/SplitSelector.h
@@ -29,7 +29,7 @@
 class SplitSelector {
 public:
     SplitSelector();
-    SplitSelector(const android::Vector<SplitDescription>& splits);
+    explicit SplitSelector(const android::Vector<SplitDescription>& splits);
 
     android::Vector<SplitDescription> getBestSplits(const SplitDescription& target) const;