content: Improve thread priority for raster threads.

content/renderer/raster_worker_pool.h

Index: content/renderer/raster_worker_pool.h
diff --git a/content/renderer/raster_worker_pool.h b/content/renderer/raster_worker_pool.h
index 1d6fc04ca6719ed8fd22f34093b7a35d3c8b4814..d0ef4b5661b360fbbe4281e245fdc0437eb40463 100644
--- a/content/renderer/raster_worker_pool.h
+++ b/content/renderer/raster_worker_pool.h
@@ -52,10 +52,10 @@ class CONTENT_EXPORT RasterWorkerPool : public base::TaskRunner,
 
   void FlushForTesting();
 
-  // Spawn |num_threads| number of threads and start running work on the
-  // worker threads.
-  void Start(int num_threads,
-             const base::SimpleThread::Options& thread_options);
+  // Spawn worker threads start running work on them. A seperate thread for
+  // background work is always created and |num_foreground_threads| the number
+  // of threads to use for foreground work.
+  void Start(int num_foreground_threads);
 
   // Finish running all the posted tasks (and nested task posted by those tasks)
   // of all the associated task runners.