Make displayAsyncThen use the CompositeAndReadbackAsync path.

content/shell/renderer/test_runner/WebTestProxy.cpp

Index: content/shell/renderer/test_runner/WebTestProxy.cpp
diff --git a/content/shell/renderer/test_runner/WebTestProxy.cpp b/content/shell/renderer/test_runner/WebTestProxy.cpp
index 02cdbd4bbe8cae3cc8e785cfb9ea9bd3cf06cbb5..e44556ddc0363e1d7e96f2434b8d7394e9a1a028 100644
--- a/content/shell/renderer/test_runner/WebTestProxy.cpp
+++ b/content/shell/renderer/test_runner/WebTestProxy.cpp
@@ -489,19 +489,23 @@ void WebTestProxyBase::didCompositeAndReadback(const SkBitmap& bitmap) {
 
 void WebTestProxyBase::CapturePixelsAsync(
     base::Callback<void(const SkBitmap&)> callback) {
-  m_compositeAndReadbackCallback = callback;
   TRACE_EVENT0("shell", "WebTestProxyBase::CapturePixelsAsync");
 
+  m_compositeAndReadbackCallback = callback;
+
   // Do a layout here because it might leave compositing mode! x.x
   // TODO(danakj): Remove this when we have kForceCompositingMode everywhere.
   webWidget()->layout();
 
-  if (!webWidget()->compositeAndReadbackAsync(this)) {
+  if (!webWidget()->isAcceleratedCompositingActive()) {

[danakj, 2014/05/05 18:35:17]

This was the only way that compositeAndReadbackAsync could return false. I'm
going to remove the bool return value and assert instead in it in a blink CL.

     TRACE_EVENT0("shell",
                  "WebTestProxyBase::CapturePixelsAsync "
-                 "compositeAndReadbackAsync failed");
+                 "isAcceleratedCompositingActive false");
     didCompositeAndReadback(SkBitmap());
+    return;
   }
+
+  webWidget()->compositeAndReadbackAsync(this);
 }
 
 void WebTestProxyBase::setLogConsoleOutput(bool enabled)
@@ -597,8 +601,7 @@ SkCanvas* WebTestProxyBase::canvas()
     return m_canvas.get();
 }
 
-void WebTestProxyBase::display(base::Closure callback)
-{
+void WebTestProxyBase::DisplayForSoftwareMode(const base::Closure& callback) {
     const blink::WebSize& size = webWidget()->size();
     WebRect rect(0, 0, size.width, size.height);
     m_paintRect = rect;
@@ -608,15 +611,33 @@ void WebTestProxyBase::display(base::Closure callback)
         callback.Run();
 }
 
+void WebTestProxyBase::DidDisplayAsync(const base::Closure& callback,
+                                       const SkBitmap& bitmap) {
+  if (!callback.is_null())
+    callback.Run();
+}
+
 void WebTestProxyBase::displayAsyncThen(base::Closure callback)
 {
-  // TODO(enne): When compositing, this should invoke a real rAF, paint,
-  // and commit.  For now, just make sure that displayAsync is actually
-  // async so that callers can't depend on synchronous behavior.
-  m_delegate->postTask(new ClosureTask(
-      this,
-      base::Bind(
-          &WebTestProxyBase::display, base::Unretained(this), callback)));
+  TRACE_EVENT0("shell", "WebTestProxyBase::displayAsyncThen");
+
+  // TODO(danakj): Just call CapturePixelsAsyc when we have
+  // kForceCompositingMode everywhere.
+
+  // Do a layout here because it might leave compositing mode! x.x
+  webWidget()->layout();
+
+  if (!webWidget()->isAcceleratedCompositingActive()) {
+    TRACE_EVENT0("shell",
+                 "WebTestProxyBase::displayAsyncThen "
+                 "isAcceleratedCompositingActive false");
+    DisplayForSoftwareMode(callback);
+    return;
+  }
+
+  m_compositeAndReadbackCallback = base::Bind(

[danakj, 2014/05/05 18:35:17]

I could call CapturePixelsAsync here instead of setting the callback and calling
compositeAndReadbackAsync directly, but then we'd do yet another layout(). wdyt?

[enne (OOO), 2014/05/05 19:55:13]

Yeah, I think that'd be cleaner.  Can you just move the layout call inside the
conditional?

A second layout shouldn't do anything wrong, I don't think.

+      &WebTestProxyBase::DidDisplayAsync, base::Unretained(this), callback);
+  webWidget()->compositeAndReadbackAsync(this);
 }
 
 void WebTestProxyBase::discardBackingStore()