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()) {

[Justin Novosad, 2015/02/13 03:00:05]

Theory on why this this CL introduced flake: drag_image_ is never reset, so it
may contain remnants of a previous test. I don't know this class very well but I
am guessing WebTestProxyBase::Reset() might be the right place. 

Also, I think you should be checking the test runner flag here to avoid falling
back to the regular pixel dump in the case where dumpDragImage was called but no
drag ever happened.  That would be an error in the test, and it should produce
an error in the test result (blank output?)

[jackhou1, 2015/02/13 04:54:44]

Yeah that does fix the flakiness: https://codereview.chromium.org/918313003/
That CL was failing on the CQ for some reason though.
I'll put together a new CL with that fix included.
Ah, good point, I'll make this change in the new CL.

+    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);