Update Blink GC plugin to reflect that Oilpan is now always enabled.

tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp

Index: tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
diff --git a/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp b/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
index b8d0a44573f8204284f0be5518308dbb0bfd89b4..7c21061e5ac18813b3d63742a5a86f5cb755827a 100644
--- a/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
+++ b/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
@@ -34,9 +34,12 @@ class BlinkGCPluginAction : public PluginASTAction {
     bool parsed = true;
 
     for (size_t i = 0; i < args.size() && parsed; ++i) {
-      if (args[i] == "enable-oilpan") {
-        options_.enable_oilpan = true;
-      } else if (args[i] == "dump-graph") {
+      // TODO(sof): remove this case once a version of the GC plugin
+      // has rolled which has enable-oilpan-always baked in _and_
+      // Blink no longer passes in the option (cf. Source/config.gyp)
+      if (args[i] == "enable-oilpan")
+        continue;
+      if (args[i] == "dump-graph") {
         options_.dump_graph = true;
       } else if (args[i] == "warn-raw-ptr") {
         options_.warn_raw_ptr = true;