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..cbcaa95030f70178e87cc616f73f35af757cda9b 100644
--- a/content/shell/renderer/test_runner/web_test_proxy.cc
+++ b/content/shell/renderer/test_runner/web_test_proxy.cc
@@ -6,6 +6,7 @@
 
 #include <cctype>
 
+#include "base/base64.h"
 #include "base/callback_helpers.h"
 #include "base/command_line.h"
 #include "base/logging.h"
@@ -806,6 +807,15 @@ void WebTestProxyBase::StartDragging(blink::WebLocalFrame* frame,
                                      blink::WebDragOperationsMask mask,
                                      const blink::WebImage& image,
                                      const blink::WebPoint& point) {
+  if (test_interfaces_->GetTestRunner()->shouldDumpDragImage()) {
+    const SkBitmap bitmap = image.getSkBitmap();
+    SkAutoLockPixels lock(bitmap);
+    std::string encoded;
+    base::Base64Encode(base::StringPiece(static_cast<char*>(bitmap.getPixels()),

[jackhou1, 2015/02/10 01:54:20]

Is there a better way to represent the image? This is sufficient for the test,
but there's no way to view the output as an image, and the expectations would
need updating if the pixel format changed.

[Justin Novosad, 2015/02/10 22:37:48]

Yeah this is not ideal. It would be much better to find a way to inject the drag
image into the test's pixel results.  Are your tests going to be outputting
multiple images, or always just one?

[jackhou1, 2015/02/11 00:08:24]

Just one. And I imagine that would be fine for any future tests of DragImage.

I'll look into dumping the image in place of pixel results. Let me know if you
have any suggestions.

+                                         bitmap.getSize()),
+                       &encoded);
+    delegate_->PrintMessage(std::string("DragImage: ") + encoded + "\n");
+  }
   // 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);