Fix google-explicit-constructor warnings in  opengl.

* Add explicit keyword to conversion constructors,
  or use NOLINT for implicit converters.
Bug: 28341362
Test: build with WITH_TIDY=1

Change-Id: I2508bb5c81e8fc7878a8ab5ee95cdf2c87729d85
diff --git a/opengl/libs/EGL/Loader.h b/opengl/libs/EGL/Loader.h
index 8cefe32..94f680e 100644
--- a/opengl/libs/EGL/Loader.h
+++ b/opengl/libs/EGL/Loader.h
@@ -46,7 +46,7 @@
         GLESv2      = 0x04
     };
     struct driver_t {
-        driver_t(void* gles);
+        explicit driver_t(void* gles);
         ~driver_t();
         status_t set(void* hnd, int32_t api);
         void* dso[3];