Add decode() functionality to image elements.

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index 936cb82806c0b9a8f1707312d1dc9a026d7a4018..3f2ab196c7b48e3b6832984ef77f652f2091c532 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -66,6 +66,7 @@
 #include "third_party/WebKit/public/web/WebKit.h"
 #include "third_party/WebKit/public/web/WebRuntimeFeatures.h"
 #include "third_party/WebKit/public/web/WebSelection.h"
+#include "third_party/skia/include/core/SkImage.h"
 #include "ui/gfx/switches.h"
 #include "ui/gl/gl_switches.h"
 #include "ui/native_theme/native_theme_features.h"
@@ -1071,6 +1072,23 @@ void RenderWidgetCompositor::setBottomControlsHeight(float height) {
   layer_tree_host_->SetBottomControlsHeight(height);
 }
 
+void RenderWidgetCompositor::RequestDecode(
+    sk_sp<SkImage> image,
+    const base::Callback<void(bool)>& callback) {
+  layer_tree_host_->QueueImageDecode(std::move(image), callback);

[pdr., 2017/05/18 03:20:10]

If javascript calls decode() twice on a loaded image, does that kick off two
independent decodes?

[vmpstr, 2017/05/18 18:51:12]

It issues two different promises and makes two different calls here, yes.
However, internally it will only do the decode if necessary. If it was already
locked by the previous decode, it will just succeed without doing work.

+
+  // If we're compositing synchronously, the SetNeedsCommit call which will be
+  // issued by |layer_tree_host_| is not going to cause a commit, due to the
+  // fact that this would make layout tests slow and cause flakiness. However,
+  // in this case we actually need a commit to transfer the decode requests to
+  // the impl side. So, force a commit to happen.
+  if (CompositeIsSynchronous()) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::Bind(&RenderWidgetCompositor::SynchronouslyComposite,
+                              weak_factory_.GetWeakPtr()));
+  }
+}
+
 void RenderWidgetCompositor::WillBeginMainFrame() {
   delegate_->WillBeginCompositorFrame();
 }