content: Implement dynamic priorities for raster threads.

cc/raster/task_graph_runner.h

Index: cc/raster/task_graph_runner.h
diff --git a/cc/raster/task_graph_runner.h b/cc/raster/task_graph_runner.h
index 23094ef5a7ef3c81a6cae0fbde931c57c11efe98..53fdea885b0801eadd0979694dede01bb695c577 100644
--- a/cc/raster/task_graph_runner.h
+++ b/cc/raster/task_graph_runner.h
@@ -15,12 +15,23 @@
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/threading/simple_thread.h"
+#include "base/time/time.h"
 #include "cc/base/cc_export.h"
+#include "cc/raster/task_category.h"
 
 namespace cc {
 
 class TaskGraphRunner;
 
+class CC_EXPORT TaskWorker {
+ public:
+  // TODO(prashant.n): Find better names.
+  virtual bool TaskSpeedup() = 0;
+  virtual bool TaskSlowdown() = 0;
+  virtual bool TaskDone() = 0;
+};
+
 // A task which can be run by a TaskGraphRunner. To run a Task, it should be
 // inserted into a TaskGraph, which can then be scheduled on the
 // TaskGraphRunner.
@@ -33,6 +44,10 @@ class CC_EXPORT Task : public base::RefCountedThreadSafe<Task> {
   // safety.
   virtual void RunOnWorkerThread() = 0;
 
+  TaskWorker* GetTaskWorker() { return worker_; }
+  void AttachTaskWorker(TaskWorker* worker);
+  void DetachTaskWorker();
+
   void WillRun();
   void DidRun();
   bool HasFinishedRunning() const;
@@ -43,10 +58,25 @@ class CC_EXPORT Task : public base::RefCountedThreadSafe<Task> {
   Task();
   virtual ~Task();
 
+  TaskWorker* worker_;
   bool will_run_;
   bool did_run_;
 };
 
+class CC_EXPORT AutoDetachTaskWorker {
+ public:
+  explicit AutoDetachTaskWorker(Task& task, TaskWorker* worker) : task_(task) {
+    DCHECK(worker);
+    task_.AttachTaskWorker(worker);
+  }
+
+  ~AutoDetachTaskWorker() { task_.DetachTaskWorker(); }
+
+ private:
+  Task& task_;
+  DISALLOW_COPY_AND_ASSIGN(AutoDetachTaskWorker);
+};
+
 // 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 category, a priority and a run count that matches the number of