Add libcxx_natvis_include to C++ BUILD.gn to Allow Windbg Hang Workaround

BUG=966676,966687

Change-Id: Icc3899aaf5483916cb5368c5a334116d1f7928ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1632712
Auto-Submit: Robert Liao <robliao@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663873}

build/config/c++/BUILD.gn

@@ -15,6 +15,11 @@ declare_args() {
   # TODO(thomasanderson): Set this to true by default once rL352899 is available
   # in MacOS's lldb.
   libcxx_abi_unstable = !((is_mac || is_ios) && is_debug && is_component_build)
+
+  # Builds libcxx Natvis into the symbols for type visualization.
+  # Set to false to workaround http://crbug.com/966676 and
+  # http://crbug.com/966687.
+  libcxx_natvis_include = true
 }
 
 # TODO(xiaohuic): https://crbug/917533 Crashes on internal ChromeOS build.
@@ -78,7 +83,9 @@ config("runtime_library") {
 
     # Add a debug visualizer for Microsoft's debuggers so that they can display
     # libc++ types well.
-    ldflags += [ "/NATVIS:" + rebase_path("libc++.natvis", root_build_dir) ]
+    if (libcxx_natvis_include) {
+      ldflags += [ "/NATVIS:" + rebase_path("libc++.natvis", root_build_dir) ]
+    }
   } else {
     cflags_cc += [
       "-nostdinc++",