Make pdfium_embeddertests link in debug component builds.

Target v8 has:

          'direct_dependent_settings': {
            'defines': [
              'V8_SHARED',
              'USING_V8_SHARED',
            ],
          },

For this to work, targets using v8 headers have to depend on v8
directly, else the V8_EXPORT macro won't work. Add a direct
dependency on v8.

BUG=none
TEST=do a debug component build of pdfium_embeddertests on Win,
should work without linker errors

R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1349843002 .
2 files changed