Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I080090d50f1a368a4e7c1a0732297bb6a295e34f
diff --git a/libs/hwui/renderthread/CanvasContext.cpp b/libs/hwui/renderthread/CanvasContext.cpp
index e6399d4..18cecc2 100644
--- a/libs/hwui/renderthread/CanvasContext.cpp
+++ b/libs/hwui/renderthread/CanvasContext.cpp
@@ -762,7 +762,7 @@
 
 class CanvasContext::FuncTaskProcessor : public TaskProcessor<bool> {
 public:
-    FuncTaskProcessor(Caches& caches)
+    explicit FuncTaskProcessor(Caches& caches)
             : TaskProcessor<bool>(&caches.tasks) {}
 
     virtual void onProcess(const sp<Task<bool> >& task) override {