Add log when Unity failed to create folder (#549)

* Add log when Unity failed to create folder

Follow up for #543. When Unity failed to create folder using Unity API
`AssetDatabase.CreateFolder()`, even with the workaround in #543, Unity
would still generate two error message and there is no way to turn it
off.

This change add an additional log after Unity API fails to inform the
user to ignore this error.

Author: chkuang-g

source/AndroidResolver/src/PlayServicesResolver.cs

@@ -2468,7 +2468,7 @@ internal static string CopyAssetAndLabel(string sourceLocation, string targetLoc
             }
 
             var targetDir = Path.GetDirectoryName(targetLocation);
-            if (!FileUtils.CreateFolder(targetDir)) {
+            if (!FileUtils.CreateFolder(targetDir, logger)) {
                 return String.Format("Failed to create folders at {0}", targetDir);
             }
 

source/VersionHandlerImpl/src/FileUtils.cs

@@ -639,7 +639,7 @@ internal static bool IsValidGuid(string guidStr) {
         /// </summary>
         /// <param name="path">Path to the file/directory that needs checking.</param>
         /// <returns>True if all folders are created successfully.</returns>
-        public static bool CreateFolder(string path) {
+        public static bool CreateFolder(string path, Google.Logger logger = null) {
             if (AssetDatabase.IsValidFolder(path)) {
                 return true;
             }
@@ -656,6 +656,20 @@ public static bool CreateFolder(string path) {
                 return true;
             }
 
+            if (logger != null) {
+                logger.Log(
+                    String.Format(
+                        "Please ignore Unity error messages similar to '{0}'.\n" +
+                        "Unable to use Unity API `AssetDatabase.CreateFolder()` to " +
+                        "create folder: '{1}'. Switch to use `Directory.CreateDirectory()` " +
+                        "instead. \n\n" +
+                        "See {2} for more information.",
+                        "*** is not a valid directory name.",
+                        path,
+                        "https://issuetracker.unity3d.com/product/unity/issues/guid/UUM-7046"),
+                    LogLevel.Info);
+            }
+
             return Directory.CreateDirectory(path) != null;
         }