[Oilpan] Migrate classes under module/webgl onto oilpan heap

Source/modules/webgl/WebGLContextGroup.h

Index: Source/modules/webgl/WebGLContextGroup.h
diff --git a/Source/modules/webgl/WebGLContextGroup.h b/Source/modules/webgl/WebGLContextGroup.h
index e5e6c8cd5e1d93a0f3eb77c9eaf1c852af05a925..c1244fc32b04b5ac0531def6f75cbdcbbe0b48fd 100644
--- a/Source/modules/webgl/WebGLContextGroup.h
+++ b/Source/modules/webgl/WebGLContextGroup.h
@@ -71,6 +71,7 @@ private:
     // WebGLContextGroup takes care of detaching the group objects if
     // the set of WebGLRenderingContextBase contexts becomes empty.
     HashSet<WebGLRenderingContextBase*> m_contexts;
+    GC_PLUGIN_IGNORE("http://crbug.com/516610")
     HashSet<WebGLSharedObject*> m_groupObjects;
 };