Make base:ReplaceFile return an informative error.

base/file_util_posix.cc

Index: base/file_util_posix.cc
diff --git a/base/file_util_posix.cc b/base/file_util_posix.cc
index 8b368127410e091eb392cf440f2bd9c50a417acd..97919ffdf055a92254879400f247e3ad5b4949a4 100644
--- a/base/file_util_posix.cc
+++ b/base/file_util_posix.cc
@@ -232,9 +232,17 @@ bool MoveUnsafe(const FilePath& from_path, const FilePath& to_path) {
   return true;
 }
 
-bool ReplaceFile(const FilePath& from_path, const FilePath& to_path) {
+bool ReplaceFile(const FilePath& from_path, const FilePath& to_path,
+                 base::PlatformFileError* error) {
+  if (error)
+    *error = base::PLATFORM_FILE_OK;
   base::ThreadRestrictions::AssertIOAllowed();
-  return (rename(from_path.value().c_str(), to_path.value().c_str()) == 0);
+  if (rename(from_path.value().c_str(), to_path.value().c_str()) != 0) {
+    if (error)
+      *error = base::ErrnoToPlatformFileError(errno);
+    return false;
+  }
+  return true;

[jar (doing other things), 2013/05/07 01:12:36]

nit: switch the order of the results around, and you won't need curlies, or
extra indent.  This also puts the common case up front, and makes reading
(across an early return) easier.

if(...)
  return true
...

 }
 
 bool CopyDirectory(const FilePath& from_path,