Add decode() functionality to image elements.

cc/trees/single_thread_proxy.cc

Index: cc/trees/single_thread_proxy.cc
diff --git a/cc/trees/single_thread_proxy.cc b/cc/trees/single_thread_proxy.cc
index 07b5afa607a72b95240466e413a98e6d880c3ae8..46ca82c04c8baa2b1aa5c81a9d3a2b514b59f048 100644
--- a/cc/trees/single_thread_proxy.cc
+++ b/cc/trees/single_thread_proxy.cc
@@ -204,12 +204,7 @@ void SingleThreadProxy::DoCommit() {
     if (scheduler_on_impl_thread_)
       scheduler_on_impl_thread_->DidCommit();
 
-    // Issue decode callbacks.
-    auto completed_decode_callbacks =
-        layer_tree_host_impl_->TakeCompletedImageDecodeCallbacks();
-    for (auto& callback : completed_decode_callbacks)
-      callback.Run();
-
+    IssueImageDecodeFinishedCallbacks();
     layer_tree_host_impl_->CommitComplete();
 
     // Commit goes directly to the active tree, but we need to synchronously
@@ -221,6 +216,15 @@ void SingleThreadProxy::DoCommit() {
   }
 }
 
+void SingleThreadProxy::IssueImageDecodeFinishedCallbacks() {
+  DCHECK(task_runner_provider_->IsImplThread());
+
+  auto completed_decode_callbacks =
+      layer_tree_host_impl_->TakeCompletedImageDecodeCallbacks();
+  for (auto& callback : completed_decode_callbacks)
+    callback.Run();
+}
+
 void SingleThreadProxy::CommitComplete() {
   // Commit complete happens on the main side after activate to satisfy any
   // SetNextCommitWaitsForActivation calls.
@@ -438,6 +442,19 @@ void SingleThreadProxy::NeedsImplSideInvalidation() {
   scheduler_on_impl_thread_->SetNeedsImplSideInvalidation();
 }
 
+void SingleThreadProxy::NotifyImageDecodeRequestFinished() {
+  // If we don't have a scheduler, then just issue the callbacks here.
+  // Otherwise, schedule a commit.
+  if (!scheduler_on_impl_thread_) {
+    DebugScopedSetMainThreadBlocked main_thread_blocked(task_runner_provider_);
+    DebugScopedSetImplThread impl(task_runner_provider_);
+
+    IssueImageDecodeFinishedCallbacks();
+    return;
+  }
+  SetNeedsCommitOnImplThread();
+}
+
 void SingleThreadProxy::CompositeImmediately(base::TimeTicks frame_begin_time) {
   TRACE_EVENT0("cc,benchmark", "SingleThreadProxy::CompositeImmediately");
   DCHECK(task_runner_provider_->IsMainThread());