Introduce the abstract class WebViewBase, to decouple WebViewImpl.

third_party/WebKit/Source/web/WebViewImpl.cpp

Index: third_party/WebKit/Source/web/WebViewImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebViewImpl.cpp b/third_party/WebKit/Source/web/WebViewImpl.cpp
index 7156fc237344bbe7bf1e894415c5b10ebd382c55..5cb5f0877bd765fc03d22d855cac2daff5b0626b 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -283,6 +283,10 @@ WebViewImpl* WebViewImpl::Create(WebViewClient* client,
   return AdoptRef(new WebViewImpl(client, visibility_state)).LeakRef();
 }
 
+const WebInputEvent* WebViewBase::CurrentInputEvent() {
+  return WebViewImpl::CurrentInputEvent();
+}
+
 void WebView::SetUseExternalPopupMenus(bool use_external_popup_menus) {
   g_should_use_external_popup_menus = use_external_popup_menus;
 }
@@ -1657,6 +1661,11 @@ WebInputEventResult WebViewImpl::SendContextMenuEvent(
         .SendContextMenuEventForKey(nullptr);
   }
 }
+#else
+WebInputEventResult WebViewImpl::SendContextMenuEvent(
+    const WebKeyboardEvent& event) {
+  return WebInputEventResult::kNotHandled;
+}
 #endif
 
 void WebViewImpl::ShowContextMenuAtPoint(float x,