win: Fix a 64bit warning.

win: Fix a 64bit warning.

clang warns:
..\..\base\files\file_path.cc(695,47) :  warning(clang): cast to 'wchar_t *' from smaller integer type 'LONG' (aka 'long') [-Wint-to-pointer-cast]
    wchar_t c1 = (wchar_t)LOWORD(::CharUpperW((LPWSTR)MAKELONG(*i1, 0)));
                                              ^

CharUpper() is a pretty whacko: It takes a pointer, but: """
A null-terminated string, or a single character. If the high-order word of this
parameter is zero, the low-order word must contain a single character to be
converted.""" (!)

It's not clear to me what this means on 64bit, but the code as-is casted a
32bit int (a DWORD) to a pointer, which I think doesn't guarantee that the
upper 4 byte of the 8 byte pointer are zero. So insert a cast to a pointer-wide
int type to guarantee this, and to fix this warning.

BUG=82385
R=brettw@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=290905

[brettw, 2014-08-20 20:09:48]

LGTM

[Nico, 2014-08-20 20:12:22]

Committed patchset #1 manually as 290905 (presubmit successful).