Prepare for -Wall for third-party code, -Wextra for chromium_code

third_party/android_protobuf/BUILD.gn

Index: third_party/android_protobuf/BUILD.gn
diff --git a/third_party/android_protobuf/BUILD.gn b/third_party/android_protobuf/BUILD.gn
index 266ca83a7ae5631ac756fc16abcefc42b28a0756..79d5c4a247a0beb83d8d5e2328e516900ab3aa75 100644
--- a/third_party/android_protobuf/BUILD.gn
+++ b/third_party/android_protobuf/BUILD.gn
@@ -3,10 +3,24 @@
 # found in the LICENSE file.
 
 if (current_toolchain == host_toolchain) {
+  config("android_protoc_warnings") {
+    cflags = [
+      "-Wno-null-conversion",
+      "-Wno-tautological-undefined-compare",
+      "-Wno-unused-function",
+      "-Wno-unused-local-typedef",
+    ]
+  }
+
   # GYP: //third_party/android_protobuf/android_protobuf.gyp:android_protoc
   executable("android_protoc") {
     configs -= [ "//build/config/compiler:chromium_code" ]
-    configs += [ "//build/config/compiler:no_chromium_code" ]
+    configs += [
+      "//build/config/compiler:no_chromium_code",
+
+      # Must be after no_chromium_code so warning flags are ordered correctly.
+      ":android_protoc_warnings",
+    ]
 
     deps = [
       "//build/config/sanitizers:deps",
@@ -114,12 +128,6 @@ if (current_toolchain == host_toolchain) {
       "src/src",
     ]
 
-    if (is_clang) {
-      cflags = [
-        "-Wno-null-conversion",
-        "-Wno-tautological-undefined-compare",
-      ]
-    }
     defines = [
       # This macro must be defined to suppress the use
       # of dynamic_cast<>, which requires RTTI.