Resolve all but two VC++ build warnings in pdfium.

pdfium.gyp

Index: pdfium.gyp
diff --git a/pdfium.gyp b/pdfium.gyp
index 0ac04715e456155a2f59eb3714ef8ef9358ad0d3..0313280e440c3d4c0f6a67dea8b4ed182702f2bc 100644
--- a/pdfium.gyp
+++ b/pdfium.gyp
@@ -308,6 +308,12 @@
       'include_dirs': [
       ],
       'ldflags': [ '-L<(PRODUCT_DIR)',],
+      'msvs_settings': {
+        'VCCLCompilerTool': {
+          # Unresolved warnings in fx_codec_jpx_opj.cpp
+          'WarnAsError': 'false',

[brucedawson, 2015/01/06 18:03:32]

Scott -- is there any better way to disable WarnAsError for
fx_codec_jpx_opj.cpp? I don't want to suppress the warning until we are more
certain whether it should be fixed.

I'm okay with this compromise solution (disabling WarnAsError for one project)
but if we can easily do it for one file, better yet.

+        },
+      },
       'sources': [
         'core/include/fxcodec/fx_codec.h',
         'core/include/fxcodec/fx_codec_def.h',