Misc fixes for gn builds with VS 2015

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 08d10a494fa019f7002074a59b999a1a7405d730..760657cedb34e6c8c0cf72bf16ea8e2254388c7f 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -753,6 +753,14 @@ config("default_warnings") {
       "/wd4459",
     ]
 
+    if (visual_studio_version == "2015") {
+      # VC++ 2015 changes 32-bit size_t truncation warnings from 4244 to 4267.
+      # Example: short TruncTest(size_t x) { return x; }
+      # Since we already disable 4244 we need to disable 4267 during migration.
+      # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
+      cflags += [ "/wd4267" ]
+    }
+
     # VS xtree header file needs to be patched or 4702 (unreachable code
     # warning) is reported if _HAS_EXCEPTIONS=0. Disable the warning if xtree is
     # not patched.