Fix google-explicit-constructor warnings in media.

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

Change-Id: I141b22bcb3caf386400b6b0403d1b231a8e7e6c4
diff --git a/media/ndk/NdkImageReaderPriv.h b/media/ndk/NdkImageReaderPriv.h
index 48f0953..8b540fa 100644
--- a/media/ndk/NdkImageReaderPriv.h
+++ b/media/ndk/NdkImageReaderPriv.h
@@ -112,7 +112,7 @@
 
     struct FrameListener : public ConsumerBase::FrameAvailableListener {
       public:
-        FrameListener(AImageReader* parent) : mReader(parent) {}
+        explicit FrameListener(AImageReader* parent) : mReader(parent) {}
 
         void onFrameAvailable(const BufferItem& item) override;