Fix LNK1210 when linking blink_core.dll in gn builds.

This matches the 'LinkIncremental': '1' for webcore_shared
in core.gyp ('1' means 'off' for LinkIncremental).

Patch dictated by scottmg over a noisy channel; typing and
denoising by me.

BUG=587530
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/1709783002 .

Cr-Commit-Position: refs/heads/master@{#376000}

third_party/WebKit/Source/core/BUILD.gn

@@ -173,6 +173,13 @@ component("core") {
     ":svg",
   ]
 
+  if (is_win && is_debug) {
+    # Incremental linking doesn't work on this target in debug mode, even
+    # with symbol_level=1.
+    configs -= [ "//build/config/win:default_incremental_linking" ]
+    configs += [ "//build/config/win:no_incremental_linking" ]
+  }
+
   public_configs = [
     ":core_include_dirs",
     ":link_core_modules_separately",