Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I7e061f68acdde368a3b63c029b928133646ebff2
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer_hwc1.cpp b/services/surfaceflinger/DisplayHardware/HWComposer_hwc1.cpp
index 4afd8a2..9d92f61 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer_hwc1.cpp
+++ b/services/surfaceflinger/DisplayHardware/HWComposer_hwc1.cpp
@@ -926,7 +926,7 @@
 protected:
     HWCTYPE* const mLayerList;
     HWCTYPE* mCurrentLayer;
-    Iterable(HWCTYPE* layer) : mLayerList(layer), mCurrentLayer(layer),
+    explicit Iterable(HWCTYPE* layer) : mLayerList(layer), mCurrentLayer(layer),
             mIndex(0) { }
     inline HWCTYPE const * getLayer() const { return mCurrentLayer; }
     inline HWCTYPE* getLayer() { return mCurrentLayer; }