Fix google-explicit-constructor warnings in media/mca.

* Add explicit keyword to conversion constructors.
Bug: 28341362
Test: build with WITH_TIDY=1

Change-Id: Ia820e0a82df4bf74e5846917f6148849aed6ddc0

media/mca/filterfw/native/core/gl_frame.h

@@ -38,7 +38,7 @@ class GLFrame : public GLBufferHandle {
     // Create an empty GL frame in the specified GL environment. Note, that the GLFrame does NOT
     // take ownership. The caller must make sure the GLEnv stays valid as long as the GLFrame is
     // alive.
-    GLFrame(GLEnv* gl_env);
+    explicit GLFrame(GLEnv* gl_env);
 
     // Deallocate a GL frame.
     ~GLFrame();

media/mca/filterfw/native/core/native_frame.h

@@ -27,7 +27,7 @@ namespace filterfw {
 class NativeFrame {
   public:
     // Create an empty native frame.
-    NativeFrame(int size);
+    explicit NativeFrame(int size);
 
     ~NativeFrame();