Make base:ReplaceFile return an informative error.

base/platform_file_posix.cc

Index: base/platform_file_posix.cc
diff --git a/base/platform_file_posix.cc b/base/platform_file_posix.cc
index fa8fc6234bed42d150b493d7e46f6fb58cc49e39..94184ab3e6eef16f3f5eadea4f4ecf93118e9ac4 100644
--- a/base/platform_file_posix.cc
+++ b/base/platform_file_posix.cc
@@ -122,39 +122,8 @@ PlatformFile CreatePlatformFileUnsafe(const FilePath& name,
   if (error) {
     if (descriptor >= 0)
       *error = PLATFORM_FILE_OK;
-    else {
-      switch (errno) {
-        case EACCES:
-        case EISDIR:
-        case EROFS:
-        case EPERM:
-          *error = PLATFORM_FILE_ERROR_ACCESS_DENIED;
-          break;
-        case ETXTBSY:
-          *error = PLATFORM_FILE_ERROR_IN_USE;
-          break;
-        case EEXIST:
-          *error = PLATFORM_FILE_ERROR_EXISTS;
-          break;
-        case ENOENT:
-          *error = PLATFORM_FILE_ERROR_NOT_FOUND;
-          break;
-        case EMFILE:
-          *error = PLATFORM_FILE_ERROR_TOO_MANY_OPENED;
-          break;
-        case ENOMEM:
-          *error = PLATFORM_FILE_ERROR_NO_MEMORY;
-          break;
-        case ENOSPC:
-          *error = PLATFORM_FILE_ERROR_NO_SPACE;
-          break;
-        case ENOTDIR:
-          *error = PLATFORM_FILE_ERROR_NOT_A_DIRECTORY;
-          break;
-        default:
-          *error = PLATFORM_FILE_ERROR_FAILED;
-      }
-    }
+    else
+      *error = ErrnoToPlatformFileError(errno);
   }
 
   return descriptor;
@@ -335,4 +304,30 @@ bool GetPlatformFileInfo(PlatformFile file, PlatformFileInfo* info) {
   return true;
 }
 
+PlatformFileError ErrnoToPlatformFileError(int saved_errno) {
+  switch (saved_errno) {
+    case EACCES:
+    case EISDIR:
+    case EROFS:
+    case EPERM:
+      return PLATFORM_FILE_ERROR_ACCESS_DENIED;
+    case ETXTBSY:
+      return PLATFORM_FILE_ERROR_IN_USE;
+    case EEXIST:
+      return PLATFORM_FILE_ERROR_EXISTS;
+    case ENOENT:
+      return PLATFORM_FILE_ERROR_NOT_FOUND;
+    case EMFILE:
+      return PLATFORM_FILE_ERROR_TOO_MANY_OPENED;
+    case ENOMEM:
+      return PLATFORM_FILE_ERROR_NO_MEMORY;
+    case ENOSPC:
+      return PLATFORM_FILE_ERROR_NO_SPACE;
+    case ENOTDIR:
+      return PLATFORM_FILE_ERROR_NOT_A_DIRECTORY;
+    default:
+      return PLATFORM_FILE_ERROR_FAILED;
+  }
+}
+
 }  // namespace base