Move Google3-specific stack limitation logic to template classes.

include/gpu/gl/GrGLInterface.h

Index: include/gpu/gl/GrGLInterface.h
diff --git a/include/gpu/gl/GrGLInterface.h b/include/gpu/gl/GrGLInterface.h
index 31429a8ebc98007faed0cb42aedf1103c9bdb293..5fa31eda944e91339716799e09d22fad1e628c02 100644
--- a/include/gpu/gl/GrGLInterface.h
+++ b/include/gpu/gl/GrGLInterface.h
@@ -109,7 +109,8 @@ private:
     template <typename FNPTR_TYPE> class GLPtr {
     public:
         GLPtr() : fPtr(NULL) {}
-        GLPtr operator=(FNPTR_TYPE ptr) { fPtr = ptr; return *this; }
+        GLPtr(const GLPtr&) = delete;
+        GLPtr& operator=(FNPTR_TYPE ptr) { fPtr = ptr; return *this; }
         operator FNPTR_TYPE() const { return fPtr; }
     private:
         FNPTR_TYPE fPtr;
@@ -119,7 +120,8 @@ private:
     // they're updated to use the Functions struct.
     template <typename FNPTR_TYPE> class GLPtrAlias {
     public:
-        GLPtrAlias(GLPtr<FNPTR_TYPE>* base) : fBase(base) {}
+        explicit GLPtrAlias(GLPtr<FNPTR_TYPE>* base) : fBase(base) {}
+        GLPtrAlias(const GLPtrAlias&) = delete;
         void operator=(FNPTR_TYPE ptr) { *fBase = ptr; }
     private:
         GLPtr<FNPTR_TYPE>* fBase;