Stop overwriting errno in base::StringPrintf, StringAppendV, and StringToDouble

Stop overwriting errno in base::StringPrintf, StringAppendV, and StringToDouble.

BUG=None
TEST=new tests added

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=198001

[Yusuke Sato, 2013-05-02 14:58:25]

Brett, could you have a look at this? This CL adds errno restoring code to
StringPrintf, StringAppendV, and StringToDouble.

Background:
I'm working on some lower layer stuff where errno is sometimes important, and
noticed that a unit test something like the following started failing after I
had inserted the (*) line:

// production code
int syscall_wrapper(...) {
  ...
  int result = real_syscall(...);
  if (result < 0)
    update_some_internal_statistics_with_string_printf();  // (*)
  return result;
}

// unit test
TEST_F(..., ...) {
  setup_syscall_mock(ENOENT);
  EXPECT_EQ(-1, syscall_wrapper(..));  // passes
  EXPECT_EQ(ENOENT, errno);  // fails since base::StringPrintf always resets
errno.
}

It would be very convenient for us if the base functions stop overwriting errno.

[brettw, 2013-05-02 18:30:18]

LGTM

https://codereview.chromium.org/14749003/diff/7003/base/scoped_clear_errno.h
File base/scoped_clear_errno.h (right):

https://codereview.chromium.org/14749003/diff/7003/base/scoped_clear_errno.h#...
base/scoped_clear_errno.h:12: // Simple scoper that saves the current value of
errno, resets it to 0, and on
Please put this file in the base namespace.

[Yusuke Sato, 2013-05-02 18:50:31]

https://codereview.chromium.org/14749003/diff/7003/base/scoped_clear_errno.h
File base/scoped_clear_errno.h (right):

https://codereview.chromium.org/14749003/diff/7003/base/scoped_clear_errno.h#...
base/scoped_clear_errno.h:12: // Simple scoper that saves the current value of
errno, resets it to 0, and on
On 2013/05/02 18:30:18, brettw wrote:
> Please put this file in the base namespace.

Done.

[commit-bot: I haz the power, 2013-05-02 18:56:46]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/yusukes@chromium.org/14749003/51001

[commit-bot: I haz the power, 2013-05-02 23:06:27]

Change committed as 198001