Enable Blink GC plugin check for stack allocated classes.

third_party/WebKit/Source/BUILD.gn

Index: third_party/WebKit/Source/BUILD.gn
diff --git a/third_party/WebKit/Source/BUILD.gn b/third_party/WebKit/Source/BUILD.gn
index ca5d37ceb669962f2b942391e9c90c4b2f0c26aa..da63271a03bbc769c3e25761e7a554fecd371b8b 100644
--- a/third_party/WebKit/Source/BUILD.gn
+++ b/third_party/WebKit/Source/BUILD.gn
@@ -29,6 +29,13 @@ declare_args() {
   # rather than legacy Blink name.
   # TODO(https://crbug.com/675879): Remove this option after the Blink rename.
   blink_gc_plugin_option_use_chromium_style_naming = false
+
+  # Set to true to have the clang Blink GC plugin additionally check if
+  # stack only classes (i.e., STACK_ALLOCATED()-annotated) define an unused
+  # and unwanted trace method.
+  # TODO(https://crbug.com/689864): remove once the GC plugin has been rolled
+  # with this check default enabled.
+  blink_gc_plugin_option_warn_stack_allocated_trace_methods = true

[Nico, 2017/03/02 14:08:56]

if the plan is to remove this soon again…

 }
 
 # features ---------------------------------------------------------------------
@@ -151,6 +158,14 @@ config("config") {
         "use-chromium-style-naming",
       ]
     }
+    if (blink_gc_plugin_option_warn_stack_allocated_trace_methods) {

[Nico, 2017/03/02 14:08:56]

…maybe just add it unconditionally here?

[sof, 2017/03/02 14:28:41]

Yes, selectively turning it off shouldn't be needed in practice. Done.

+      cflags += [
+        "-Xclang",
+        "-plugin-arg-blink-gc-plugin",
+        "-Xclang",
+        "warn-stack-allocated-trace-method",
+      ]
+    }
   }
 }