Oilpan: have WebRemoteFrameImpl use SelfKeepAlive<>.

Source/web/WebRemoteFrameImpl.h

Index: Source/web/WebRemoteFrameImpl.h
diff --git a/Source/web/WebRemoteFrameImpl.h b/Source/web/WebRemoteFrameImpl.h
index 034253236c2cd631f44c4ff8eca72333cfb871d4..f197680131cbd39f8f64f2cd8782ba5a7b09ebf2 100644
--- a/Source/web/WebRemoteFrameImpl.h
+++ b/Source/web/WebRemoteFrameImpl.h
@@ -202,14 +202,10 @@ private:
     WillBeHeapHashMap<WebFrame*, OwnPtrWillBeMember<FrameOwner>> m_ownersForChildren;
 
 #if ENABLE(OILPAN)
-    // Oilpan: to provide the guarantee of having the frame live until
-    // close() is called, an instance keep a self-persistent. It is
-    // cleared upon calling close(). This avoids having to assume that
-    // an embedder's WebFrame references are all discovered via thread
-    // state (stack, registers) should an Oilpan GC strike while we're
-    // in the process of detaching.
-    GC_PLUGIN_IGNORE("340522")
-    Persistent<WebRemoteFrameImpl> m_selfKeepAlive;
+    // Oilpan: WebRemoteFrameImpl must remain alive until close() is called.
+    // Accomplish that by keeping a self-referential Persistent<>. It is
+    // cleared upon close().
+    SelfKeepAlive<WebRemoteFrameImpl> m_selfKeepAlive;
 #endif
 };