gn: make some warning flags match gyp more closely

breakpad/BUILD.gn

Index: breakpad/BUILD.gn
diff --git a/breakpad/BUILD.gn b/breakpad/BUILD.gn
index 899cfef080e317485b3394c2b42d64f2c7e3408e..68eb059218e3cdb06b0f79f189d95e353668b813 100644
--- a/breakpad/BUILD.gn
+++ b/breakpad/BUILD.gn
@@ -145,6 +145,10 @@ if (current_toolchain == host_toolchain && !is_win) {
     ]
 
     configs += [ ":tools_config" ]
+
+    # There are some warnings in this code.
+    configs -= [ "//build/config/compiler:chromium_code" ]
+    configs += [ "//build/config/compiler:no_chromium_code" ]
   }
 }
 
@@ -478,6 +482,10 @@ if (is_linux) {
       "src/third_party/linux/include",
       ".",
     ]
+
+    # There are some warnings in this code.
+    configs -= [ "//build/config/compiler:chromium_code" ]
+    configs += [ "//build/config/compiler:no_chromium_code" ]
   }
 
   test("breakpad_unittests") {