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

third_party/WebKit/Source/platform/BUILD.gn

Index: third_party/WebKit/Source/platform/BUILD.gn
diff --git a/third_party/WebKit/Source/platform/BUILD.gn b/third_party/WebKit/Source/platform/BUILD.gn
index d45fa60f61b735f57de7498d307ca52ad149ee75..bf09f90de07c142b08bd993876f054cce69b66aa 100644
--- a/third_party/WebKit/Source/platform/BUILD.gn
+++ b/third_party/WebKit/Source/platform/BUILD.gn
@@ -1514,6 +1514,14 @@ component("platform") {
       "/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",