Re-land: cc: Add raster finished signals to RasterWorkerPool.

cc/test/layer_tree_test.cc

Index: cc/test/layer_tree_test.cc
diff --git a/cc/test/layer_tree_test.cc b/cc/test/layer_tree_test.cc
index 1d4a79795d1e8ab31cd8e1dbc3b7b741ba0864f7..6a435054de7ac35a4b4c8ebecb37133862bbe417 100644
--- a/cc/test/layer_tree_test.cc
+++ b/cc/test/layer_tree_test.cc
@@ -41,6 +41,10 @@ bool TestHooks::CanActivatePendingTree(LayerTreeHostImpl* host_impl) {
   return true;
 }
 
+bool TestHooks::CanActivatePendingTreeIfNeeded(LayerTreeHostImpl* host_impl) {
+  return true;
+}
+
 // Adapts LayerTreeHostImpl for test. Runs real code, then invokes test hooks.
 class LayerTreeHostImplForTesting : public LayerTreeHostImpl {
  public:
@@ -114,7 +118,7 @@ class LayerTreeHostImplForTesting : public LayerTreeHostImpl {
     if (!pending_tree())
       return;
 
-    if (!test_hooks_->CanActivatePendingTree(this))
+    if (!test_hooks_->CanActivatePendingTreeIfNeeded(this))
       return;
 
     LayerTreeHostImpl::ActivatePendingTreeIfNeeded();