chromium_code tweaks for Windows and Linux/gyp.

BUG=pdfium:29
R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1431563002 .
diff --git a/BUILD.gn b/BUILD.gn
index fa6c906..3e1b89c 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -38,6 +38,12 @@
       "/wd4146",
       "/wd4333",
       "/wd4345",
+      # TODO(thestig): Fix all instances, remove this, pdfium:29
+      "/wd4245",
+      "/wd4389",
+      "/wd4701",
+      "/wd4706",
+      "/wd4800",
     ]
   }
 
diff --git a/pdfium.gyp b/pdfium.gyp
index 8788794..5637dbb 100644
--- a/pdfium.gyp
+++ b/pdfium.gyp
@@ -41,13 +41,17 @@
       }],
     ],
     'msvs_disabled_warnings': [
-      4005, 4018, 4146, 4333, 4345, 4267
+      4005, 4018, 4146, 4333, 4345, 4267,
+      # TODO(thestig): Fix all instances, remove this, pdfium:29
+      4245, 4389, 4701, 4706, 4800,
     ],
     'variables': {
       'clang_warning_flags': [
         # TODO(thestig): Fix all instances, remove this, pdfium:29
         '-Wno-sign-compare',
       ],
+      # Make sure Chromium's build/common.gypi doesn't re-add the flag on linux.
+      'cflags_cc!': [ '-Wsign-compare' ],
     },
   },
   'targets': [