Use the /WX flag to have link warnings treated as errors.

third_party/WebKit/Source/platform/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//testing/libfuzzer/fuzzer_test.gni")
 import("//testing/test.gni")
 import("//third_party/WebKit/public/public_features.gni")
 import("//third_party/WebKit/Source/build/scripts/scripts.gni")
@@ skipping 1496 matching lines @@
       "clipboard/ClipboardUtilitiesPosix.cpp",
 
       # Uses LocaleWin instead.
       "text/LocaleICU.cpp",
       "text/LocaleICU.h",
     ]
     cflags = [
       "/wd4334",  # Result of 32-bit shift implicitly converted to 64 bits.
       "/wd4724",  # Modulo by 0.
     ]
+
+    # crbug.com/654776: Suppress symbol import warnings.
+    if (is_component_build) {
+      ldflags = [
+        "/ignore:4217",
+        "/ignore:4049",
+      ]
+    }
   } else {
     sources -= [
       "clipboard/ClipboardUtilitiesWin.cpp",
       "text/LocaleWin.cpp",
     ]
   }
 
   if (is_android) {
     # Add in some Linux files also shared with Android.
     set_sources_assignment_filter([])
@@ skipping 543 matching lines @@
     "//third_party/WebKit/Source:config",
     "//third_party/WebKit/Source:inside_blink",
   ]
 
   deps = [
     ":test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }