TaskGraphRunner Group support

cc/raster/task_graph_runner.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_RASTER_TASK_GRAPH_RUNNER_H_
 #define CC_RASTER_TASK_GRAPH_RUNNER_H_
 
 #include <algorithm>
 #include <map>
 #include <vector>
@@ skipping 28 matching lines @@
 
   Task();
   virtual ~Task();
 
   bool will_run_;
   bool did_run_;
 };
 
 // A task dependency graph describes the order in which to execute a set
 // of tasks. Dependencies are represented as edges. Each node is assigned
-// a priority and a run count that matches the number of dependencies.
-// Priority range from 0 (most favorable scheduling) to UINT_MAX
-// (least favorable).
+// a category, a priority and a run count that matches the number of
+// dependencies. Priority range from 0 (most favorable scheduling) to UINT16_MAX
+// (least favorable). Categories range from 0 to UINT16_MAX. It is up to the
+// implementation and its consumer to determine the meaning (if any) of a
+// category. A TaskGraphRunner implementation may chose to prioritize certain
+// categories over others, regardless of the individual priorities of tasks.
 struct CC_EXPORT TaskGraph {
   struct Node {
     typedef std::vector<Node> Vector;
 
-    Node(Task* task, size_t priority, size_t dependencies)
-        : task(task), priority(priority), dependencies(dependencies) {}
+    Node(Task* task,
+         uint16_t category,
+         uint16_t priority,
+         uint32_t dependencies)
+        : task(task),
+          category(category),
+          priority(priority),
+          dependencies(dependencies) {}
 
     Task* task;
-    size_t priority;
-    size_t dependencies;
+    uint16_t category;
+    uint16_t priority;
+    uint32_t dependencies;
   };
 
   struct Edge {
     typedef std::vector<Edge> Vector;
 
     Edge(const Task* task, Task* dependent)
         : task(task), dependent(dependent) {}
 
     const Task* task;
     Task* dependent;
@@ skipping 131 matching lines @@
  private:
   TaskGraph* graph_;
   const Task* task_;
   size_t current_index_;
   TaskGraph::Node* current_node_;
 };
 
 }  // namespace cc
 
 #endif  // CC_RASTER_TASK_GRAPH_RUNNER_H_