Windows: Fix --enable-logging to not disable logging when stderr is a pipe

Windows: Fix --enable-logging to not disable logging when stderr is a pipe

Before this change, when chrome.exe is run under Buildbot or under
Cygwin's default terminal (mintty), passing --enable-logging (which
calls RouteStdioToConsole()) has the unfortunate side effect of
disabling logging from the browser process.  In these cases, stderr is
a pipe handle, not a Windows console, and opening CONOUT$ gives a
console handle whose output doesn't go anywhere.

(Note that this does not apply to browser_tests.exe, which has
subsystem=console in its headers.  In this case, the browser process
is already attached to a non-visible console at startup, and
RouteStdioToConsole() exits via the ERROR_ACCESS_DENIED path.)

We fix this by making RouteStdioToConsole() a no-op if stdout/stderr
already point to valid streams.

BUG=169941
TEST=Ran chrome.exe and browser_tests.exe from both Cygwin mintty and
  the Windows console, with some extra logging added; checked that
  logging is displayed.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=178656

[Mark Seaborn, 2013-01-24 18:22:21]

(Sending to original authors/reviewers of
https://chromiumcodereview.appspot.com/10832309)

[M-A Ruel, 2013-01-24 18:25:53]

Not that I'm an owner but it makes sense, lgtm

[brettw, 2013-01-24 21:36:19]

LGTM rubberstamp based on maruel's review.

[jbates, 2013-01-24 21:44:31]

lgtm