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 6a48968a73f395f11d48dd8613817d147d396a1a..68d243c7a5dab1c269c13595ac0786686a634a9b 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -284,6 +284,10 @@ 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;
 }