cc: Implement states for Task for stricter control.

cc/raster/task_graph_work_queue.cc

Index: cc/raster/task_graph_work_queue.cc
diff --git a/cc/raster/task_graph_work_queue.cc b/cc/raster/task_graph_work_queue.cc
index aa7565473aec4c35e08d9c007db6d9c8c6d38499..807539db8e49252a01c6b346a625525c7d326d85 100644
--- a/cc/raster/task_graph_work_queue.cc
+++ b/cc/raster/task_graph_work_queue.cc
@@ -144,6 +144,11 @@ void TaskGraphWorkQueue::ScheduleTasks(NamespaceToken token, TaskGraph* graph) {
         });
     if (old_it != task_namespace.graph.nodes.end()) {
       std::swap(*old_it, task_namespace.graph.nodes.back());
+      // If old task is scheduled to run again and not yet started running,
+      // reset its state to initial state as it has to be inserted in new
+      // |ready_to_run_tasks|, where it gets scheduled.
+      if (node.task->state().IsScheduled())
+        node.task->state().Reset();
       task_namespace.graph.nodes.pop_back();
     }
 
@@ -152,7 +157,7 @@ void TaskGraphWorkQueue::ScheduleTasks(NamespaceToken token, TaskGraph* graph) {
       continue;
 
     // Skip if already finished running task.
-    if (node.task->HasFinishedRunning())
+    if (node.task->state().IsFinished())
       continue;
 
     // Skip if already running.
@@ -163,6 +168,7 @@ void TaskGraphWorkQueue::ScheduleTasks(NamespaceToken token, TaskGraph* graph) {
                     }))
       continue;
 
+    node.task->state().DidSchedule();
     task_namespace.ready_to_run_tasks[node.category].push_back(PrioritizedTask(
         node.task, &task_namespace, node.category, node.priority));
   }
@@ -184,7 +190,7 @@ void TaskGraphWorkQueue::ScheduleTasks(NamespaceToken token, TaskGraph* graph) {
     TaskGraph::Node& node = *it;
 
     // Skip if already finished running task.
-    if (node.task->HasFinishedRunning())
+    if (node.task->state().IsFinished())
       continue;
 
     // Skip if already running.
@@ -198,6 +204,7 @@ void TaskGraphWorkQueue::ScheduleTasks(NamespaceToken token, TaskGraph* graph) {
     DCHECK(std::find(task_namespace.completed_tasks.begin(),
                      task_namespace.completed_tasks.end(),
                      node.task) == task_namespace.completed_tasks.end());
+    node.task->state().DidCancel();
     task_namespace.completed_tasks.push_back(node.task);
   }
 
@@ -258,6 +265,7 @@ TaskGraphWorkQueue::PrioritizedTask TaskGraphWorkQueue::GetNextTaskToRun(
   }
 
   // Add task to |running_tasks|.
+  task.task->state().DidStart();
   task_namespace->running_tasks.push_back(
       std::make_pair(task.category, task.task));
 
@@ -292,6 +300,7 @@ void TaskGraphWorkQueue::CompleteTask(const PrioritizedTask& completed_task) {
           task_namespace->ready_to_run_tasks[dependent_node.category];
 
       bool was_empty = ready_to_run_tasks.empty();
+      dependent_node.task->state().DidSchedule();
       ready_to_run_tasks.push_back(
           PrioritizedTask(dependent_node.task, task_namespace,
                           dependent_node.category, dependent_node.priority));
@@ -326,6 +335,7 @@ void TaskGraphWorkQueue::CompleteTask(const PrioritizedTask& completed_task) {
   }
 
   // Finally add task to |completed_tasks_|.
+  task->state().DidFinish();
   task_namespace->completed_tasks.push_back(task);
 }