Add more error printing to know why command buffer lib failed to load.

src/ports/SkOSLibrary_posix.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkTypes.h"
 #if !defined(SK_BUILD_FOR_WIN32)
 
 #include "SkOSLibrary.h"
 
 #include <dlfcn.h>
 
 void* DynamicLoadLibrary(const char* libraryName) {
-    return dlopen(libraryName, RTLD_LAZY);
+    void* result = dlopen(libraryName, RTLD_LAZY);
+    if (!result) {
+        SkDebugf("Error loading %s {\n %s\n}\n", libraryName, dlerror());
+    }
+    return result;
 }
 
 void* GetProcedureAddress(void* library, const char* functionName) {
     return dlsym(library, functionName);
 }
 #endif//!defined(SK_BUILD_FOR_WIN32)