Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: Ibdd6a210bb7ff228e3624cc319169f77aca3b51e
diff --git a/core/jni/android/graphics/Bitmap.cpp b/core/jni/android/graphics/Bitmap.cpp
index a805b6d..167294e 100755
--- a/core/jni/android/graphics/Bitmap.cpp
+++ b/core/jni/android/graphics/Bitmap.cpp
@@ -380,7 +380,7 @@
 // on the caller already having a local JNI ref
 class LocalScopedBitmap {
 public:
-    LocalScopedBitmap(jlong bitmapHandle)
+    explicit LocalScopedBitmap(jlong bitmapHandle)
             : mBitmap(reinterpret_cast<Bitmap*>(bitmapHandle)) {}
 
     Bitmap* operator->() {