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

cc/trees/layer_tree_host_unittest.cc

Index: cc/trees/layer_tree_host_unittest.cc
diff --git a/cc/trees/layer_tree_host_unittest.cc b/cc/trees/layer_tree_host_unittest.cc
index 1b10e416421115196994167c37e81b5e48f0e612..dde351fe53d767dd4d74054847bfb14fd508824b 100644
--- a/cc/trees/layer_tree_host_unittest.cc
+++ b/cc/trees/layer_tree_host_unittest.cc
@@ -750,6 +750,14 @@ class LayerTreeHostTestFrameTimeUpdatesAfterActivationFails
   }
 
   virtual bool CanActivatePendingTree(LayerTreeHostImpl* impl) OVERRIDE {
+    if (frame_ >= 1)
+      return true;
+
+    return false;
+  }
+
+  virtual bool CanActivatePendingTreeIfNeeded(LayerTreeHostImpl* impl)
+      OVERRIDE {
     frame_++;
     if (frame_ == 1) {
       first_frame_time_ = impl->CurrentFrameTimeTicks();