Add test_runner hook to dump drag image.

content/shell/renderer/test_runner/web_test_proxy.cc

Index: content/shell/renderer/test_runner/web_test_proxy.cc
diff --git a/content/shell/renderer/test_runner/web_test_proxy.cc b/content/shell/renderer/test_runner/web_test_proxy.cc
index da62fc05f003e2c24df25866a0e3c31f7676eddf..32a0cf0f2385581eff58518582652f03f283ca23 100644
--- a/content/shell/renderer/test_runner/web_test_proxy.cc
+++ b/content/shell/renderer/test_runner/web_test_proxy.cc
@@ -565,6 +565,11 @@ void WebTestProxyBase::CapturePixelsAsync(
   TRACE_EVENT0("shell", "WebTestProxyBase::CapturePixelsAsync");
   DCHECK(!callback.is_null());
 
+  if (!drag_image_.isNull()) {
+    callback.Run(drag_image_.getSkBitmap());
+    return;
+  }
+
   if (test_interfaces_->GetTestRunner()->isPrinting()) {
     base::MessageLoopProxy::current()->PostTask(
         FROM_HERE,
@@ -806,6 +811,10 @@ void WebTestProxyBase::StartDragging(blink::WebLocalFrame* frame,
                                      blink::WebDragOperationsMask mask,
                                      const blink::WebImage& image,
                                      const blink::WebPoint& point) {
+  if (test_interfaces_->GetTestRunner()->shouldDumpDragImage()) {
+    if (drag_image_.isNull())
+      drag_image_ = image;
+  }
   // When running a test, we need to fake a drag drop operation otherwise
   // Windows waits for real mouse events to know when the drag is over.
   test_interfaces_->GetEventSender()->DoDragDrop(data, mask);