Fix/suppress hwui/tests google-explicit-constructor warnings

* Add explicit to conversion constructors/operators

Bug: 28341362
Test: make with WITH_TIDY=1 DEFAULT_GLOBAL_TIDY_CHECKS=-*,google-explicit-constructor
Change-Id: I59c61af29ab09209c5a4c2bf43b10215bf59756a
diff --git a/libs/hwui/tests/unit/SkiaRenderPropertiesTests.cpp b/libs/hwui/tests/unit/SkiaRenderPropertiesTests.cpp
index ad5fdac..7deb0b1 100644
--- a/libs/hwui/tests/unit/SkiaRenderPropertiesTests.cpp
+++ b/libs/hwui/tests/unit/SkiaRenderPropertiesTests.cpp
@@ -45,7 +45,7 @@
     static const int CANVAS_HEIGHT = 100;
     class PropertyTestCanvas : public TestCanvasBase {
     public:
-        PropertyTestCanvas(std::function<void(const SkCanvas&)> callback)
+        explicit PropertyTestCanvas(std::function<void(const SkCanvas&)> callback)
                 : TestCanvasBase(CANVAS_WIDTH, CANVAS_HEIGHT), mCallback(callback) {}
         void onDrawRect(const SkRect& rect, const SkPaint& paint) override {
             EXPECT_EQ(mDrawCounter++, 0);