content: Implement dynamic priorities for raster threads.

base/threading/simple_thread.h

Index: base/threading/simple_thread.h
diff --git a/base/threading/simple_thread.h b/base/threading/simple_thread.h
index 3deeb1018cb573c3f5e48d2b17b7c16a428aa476..cedd3042795a54a59dfa8dccbef712fc618629e7 100644
--- a/base/threading/simple_thread.h
+++ b/base/threading/simple_thread.h
@@ -112,6 +112,12 @@ class BASE_EXPORT SimpleThread : public PlatformThread::Delegate {
   // Overridden from PlatformThread::Delegate:
   void ThreadMain() override;
 
+  // Set the priority of this thread.
+  bool SetThreadPriority(ThreadPriority priority);
+
+  // Get the priority of this thread.
+  ThreadPriority GetThreadPriority() { return priority_; }
+
  private:
   const std::string name_prefix_;
   std::string name_;
@@ -120,6 +126,46 @@ class BASE_EXPORT SimpleThread : public PlatformThread::Delegate {
   WaitableEvent event_;          // Signaled if Start() was ever called.
   PlatformThreadId tid_;         // The backing thread's id.
   bool joined_;                  // True if Join has been called.
+  ThreadPriority priority_;      // Stores currently set priority.
+};
+
+// This class creates a simple thread with capability of changing priority
+// when it is scheduled. Thread starts with |default_priority| from
+// |priorities_| and it must be started to change the priority.
+class BASE_EXPORT DynamicPriorityThread : public SimpleThread {
+ public:
+  struct BASE_EXPORT PrioritySet {
+    explicit PrioritySet(const ThreadPriority default_prio,
+                         const ThreadPriority lower_prio,
+                         const ThreadPriority higher_prio)
+        : default_priority(default_prio),
+          lower_priority(lower_prio),
+          higher_priority(higher_prio) {}
+    const ThreadPriority default_priority;
+    const ThreadPriority lower_priority;
+    const ThreadPriority higher_priority;
+  };
+
+  explicit DynamicPriorityThread(const PrioritySet& priorities,
+                                 const std::string& name_prefix,
+                                 const Options& options);
+
+  // Sets higher priority from |priorities_|.
+  bool Speedup();
+  // Sets lower priority from |priorities_|.
+  bool Slowdown();
+  // Sets default priority from |priorities_|.
+  bool RestoreDefaultPriority();
+
+  // Returns true if thread is having lower and higher priorities different.
+  bool HasDynamicPriorities() { return dynamic_priorities_; }
+
+  ThreadPriority GetDefaultPriority() { return priorities_.default_priority; }
+
+ private:
+  const PrioritySet priorities_;
+  bool dynamic_priorities_;
+  bool priority_changed_;
 };
 
 class BASE_EXPORT DelegateSimpleThread : public SimpleThread {