Fix clang-tidy warnings in libs/hwui.

* Add explicit keyword to conversion constructors.
Bug: 28341362
* Use const reference type for read-only parameters.
Bug: 30407689
Test: build with WITH_TIDY=1

Change-Id: Iab3e6636f60a70cb124f29dc19f20f842fa8dfda
diff --git a/libs/hwui/renderstate/RenderState.h b/libs/hwui/renderstate/RenderState.h
index 731d9bb..9e0fb12 100644
--- a/libs/hwui/renderstate/RenderState.h
+++ b/libs/hwui/renderstate/RenderState.h
@@ -106,7 +106,7 @@
     void interruptForFunctorInvoke();
     void resumeFromFunctorInvoke();
 
-    RenderState(renderthread::RenderThread& thread);
+    explicit RenderState(renderthread::RenderThread& thread);
     ~RenderState();