Require the result of StringPrintf to be used.

Require the result of StringPrintf to be used.

When refactoring code it is easy to accidentally disregard the output of
base::StringPrintf. The code will still look superficially correct, and may even
pass code review (as happened with https://codereview.chromium.org/436133002/ ).

This type of bug can be prevented by annotating StringPrintf with
WARN_UNUSED_RESULT. Despite the name, this causes a compile error in our build
configuration (except on Windows, where it is ignored). This should ensure that
such errors are caught by the CQ if not sooner.

TEST=build all; base_unittests
BUG=400663
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=288353

[Adam Rice, 2014-08-06 03:34:23]

PTAL

[darin (slow to review), 2014-08-06 20:33:06]

On 2014/08/06 03:34:23, Adam Rice wrote:
> PTAL

Can you please clearly summarize the problem you are solving in the description
of this CL? I followed the link to the other CL, but it is not obvious to me
what the problem was.

[Adam Rice, 2014-08-07 03:53:09]

On 2014/08/06 20:33:06, darin wrote:
> Can you please clearly summarize the problem you are solving in the
description
> of this CL? I followed the link to the other CL, but it is not obvious to me
> what the problem was.

Sorry. I have tried to clarify the description.

In the case of https://codereview.chromium.org/436133002/ the problem was not
caught until it broke the Blink layout tests. The Blink gardener tracked down
the
cause and contacted me to revert.

[darin (slow to review), 2014-08-07 21:51:15]

On 2014/08/07 03:53:09, Adam Rice wrote:
> On 2014/08/06 20:33:06, darin wrote:
> > Can you please clearly summarize the problem you are solving in the
> description
> > of this CL? I followed the link to the other CL, but it is not obvious to me
> > what the problem was.
> 
> Sorry. I have tried to clarify the description.
> 
> In the case of https://codereview.chromium.org/436133002/ the problem was not
> caught until it broke the Blink layout tests. The Blink gardener tracked down
> the
> cause and contacted me to revert.

I see. You are saying that it was a logic error to ignore the result. OK.

[darin (slow to review), 2014-08-07 21:51:43]

LGTM

[Adam Rice, 2014-08-08 13:02:58]

The CQ bit was checked by ricea@chromium.org

[commit-bot: I haz the power, 2014-08-08 13:03:58]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ricea@chromium.org/440013003/1

[commit-bot: I haz the power, 2014-08-08 14:11:59]

Change committed as 288353