Improve Visual Studio debug visualizers

tools/win/DebugVisualizers/BUILD.gn

+# Copyright 2017 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.
+
+# The .natvis files define "native visualizers" for the Visual Studio debugger
+# that allow one to define how custom types appear.
+#
+# One can use them by adding them to a project in visual studio, and they can
+# be embedded in a project's PDB file using the undocumented linker flag
+# /NATVIS. These configs would generally be added to all_dependent_configs
+# on a target so all targets that link to them will reference the visualizers
+# from their PDB files.
+#
+# See https://msdn.microsoft.com/en-us/library/jj620914.aspx for how they work.
+#
+# Since these only add ldflags, the targets themselves are not rebuilt when the
+# natvis files are updated. To debug, erase the .pdb file and build to re-link.
+
+assert(is_win)
+
+config("chrome") {
+  ldflags = [ "/NATVIS:" + rebase_path("chrome.natvis", root_build_dir) ]
+}
+
+config("skia") {
+  ldflags = [ "/NATVIS:" + rebase_path("skia.natvis", root_build_dir) ]
+}
+
+config("webkit") {
+  ldflags = [ "/NATVIS:" + rebase_path("webkit.natvis", root_build_dir) ]
+}