Introduce WebRemoteFrameBase to break dependencies on WebRemoteFrameImpl.

third_party/WebKit/Source/web/WebRemoteFrameImpl.cpp

Index: third_party/WebKit/Source/web/WebRemoteFrameImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebRemoteFrameImpl.cpp b/third_party/WebKit/Source/web/WebRemoteFrameImpl.cpp
index c9c5d51561a8f472835e2e2d52592a03e9dd0bbf..2aef3722eaac709e12a31a2d897c09d9d011cc1f 100644
--- a/third_party/WebKit/Source/web/WebRemoteFrameImpl.cpp
+++ b/third_party/WebKit/Source/web/WebRemoteFrameImpl.cpp
@@ -51,6 +51,7 @@ WebRemoteFrameImpl::~WebRemoteFrameImpl() {}
 DEFINE_TRACE(WebRemoteFrameImpl) {
   visitor->Trace(frame_client_);
   visitor->Trace(frame_);
+  WebRemoteFrameBase::Trace(visitor);
   WebFrame::TraceFrames(visitor, this);
 }
 
@@ -532,7 +533,7 @@ v8::Local<v8::Object> WebRemoteFrameImpl::GlobalProxy() const {
 
 WebRemoteFrameImpl::WebRemoteFrameImpl(WebTreeScopeType scope,
                                        WebRemoteFrameClient* client)
-    : WebRemoteFrame(scope),
+    : WebRemoteFrameBase(scope),
       frame_client_(RemoteFrameClientImpl::Create(this)),
       client_(client),
       self_keep_alive_(this) {}