win: various porting for http_body_test.cc
win: various porting for http_body_test.cc

- Wrap constants in FILE_PATH_LITERAL for L"".
- dynamic allocation, as VS otherwise complains about lack of constant
expression:

d:\src\crashpad\crashpad\util\net\http_body_test.cc(182) : error C2057: expected constant expression
d:\src\crashpad\crashpad\util\net\http_body_test.cc(182) : error C2466: cannot allocate an array of constant size 0
d:\src\crashpad\crashpad\util\net\http_body_test.cc(182) : error C2133: 'buf' : unknown size
d:\src\crashpad\crashpad\util\net\http_body_test.cc(183) : error C2070: 'uint8_t []': illegal sizeof operand
d:\src\crashpad\crashpad\util\net\http_body_test.cc(196) : error C2070: 'uint8_t []': illegal sizeof operand

R=mark@chromium.org
BUG=crashpad:1

Review URL: https://codereview.chromium.org/837293002

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