cc: Refactor additional code from BuildRasterQueue.

cc/resources/tile_manager.cc

Index: cc/resources/tile_manager.cc
diff --git a/cc/resources/tile_manager.cc b/cc/resources/tile_manager.cc
index f5c61f3d6e33b7d97e086e47730889a61576fd1e..1e2cfc1da5b728b277f2784d826f0a40e112bca4 100644
--- a/cc/resources/tile_manager.cc
+++ b/cc/resources/tile_manager.cc
@@ -362,6 +362,11 @@ void TileManager::PrepareTiles(
     scoped_ptr<RasterTilePriorityQueue> raster_priority_queue(
         client_->BuildRasterQueue(global_state_.tree_priority,
                                   RasterTilePriorityQueue::Type::ALL));
+    // Inform the client that will likely require a draw if the top tile is
+    // required for draw.
+    client_->SetIsLikelyToRequireADraw(

[vmpstr, 2015/01/26 22:08:35]

I think this is the only spot that makes sense we add this call. Alternatively,
we can add it to every spot that rebuilds the raster queue. That, however, is
iffy since some of the calls are almost certainly will set this to false
(scheduling more work after the initial batch is done) and some don't really
make sense to me (building it with intent of marking tiles rasterize on demand).

[danakj, 2015/01/29 22:33:20]

Once the initial batch of work is done, if the top of the queue is not required,
we should tell the LTHI so and stop queuing frames tho?

[vmpstr, 2015/01/29 22:48:09]

Well.. I don't think so... I mean when we draw, we will reset the flag until its
set again. So suppose the situation is that we queue 1 tiles that is required to
draw, so we SetIsLikelyToRequireDraw but then it finishes really quickly and we
get to the reschedule and find that the top tile is not required. I think in
that case, we should leave the flag whatever it was, no? If we had it at
is_likely_to_draw_ = true, then that's still the case since we finished a now
tile and didn't have a draw yet, and if it's false then leave it at false.

[danakj, 2015/01/29 23:05:34]

well, i'm not sure it matters but take a look at LTHI::NotifyReadyToDraw(). When
a tile becomes ready, we SetNeedsRedraw then and stop doing it in
WillBeginFrame. If there was only one tile then we'd have already set it to
false. So I guess this is good. Less codepaths to follow with same result.

+        !raster_priority_queue->IsEmpty() &&
+        raster_priority_queue->Top()->required_for_draw());
     AssignGpuMemoryToTiles(raster_priority_queue.get(),
                            scheduled_raster_task_limit_,
                            &tiles_that_need_to_be_rasterized);