Fix google-explicit-constructor warnings in camera.

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

Change-Id: I61f9b5b2b6e13e0c6561327bc8dfe69c9cfc5ba5
diff --git a/camera/ndk/impl/ACaptureRequest.h b/camera/ndk/impl/ACaptureRequest.h
index 6bd8406..3ef6a84 100644
--- a/camera/ndk/impl/ACaptureRequest.h
+++ b/camera/ndk/impl/ACaptureRequest.h
@@ -22,7 +22,7 @@
 using namespace android;
 
 struct ACameraOutputTarget {
-    ACameraOutputTarget(ANativeWindow* window) : mWindow(window) {};
+    explicit ACameraOutputTarget(ANativeWindow* window) : mWindow(window) {};
 
     bool operator == (const ACameraOutputTarget& other) const {
         return mWindow == other.mWindow;