Drag-and-drop: Move updateDragCursor to RenderWidgetHost.

This patch is part of the effort to transition D&D functions to all be
widget-based instead of view-based. This is necessary in order to allow
D&D to work with out-of-process iframes.

BUG=647249, 655063
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2503563002
Cr-Commit-Position: refs/heads/master@{#431997}
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 367951ac..22b6935 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -2488,6 +2488,12 @@
   return text_input_manager_.get();
 }
 
+bool WebContentsImpl::OnUpdateDragCursor() {
+  if (browser_plugin_embedder_)
+    return browser_plugin_embedder_->OnUpdateDragCursor();
+  return false;
+}
+
 BrowserAccessibilityManager*
     WebContentsImpl::GetRootBrowserAccessibilityManager() {
   RenderFrameHostImpl* rfh = GetMainFrame();