cc: Rasterize cheap tiles immediately

cc/layer_tree_host_impl.cc

Index: cc/layer_tree_host_impl.cc
diff --git a/cc/layer_tree_host_impl.cc b/cc/layer_tree_host_impl.cc
index 607a50c2344ce9bc1810702f5238d2507b535de4..5eee47e3803ba29969bcb886f2644345e0ea6253 100644
--- a/cc/layer_tree_host_impl.cc
+++ b/cc/layer_tree_host_impl.cc
@@ -48,6 +48,12 @@
 
 namespace {
 
+// Limits for the total number of cheap tile rasterizations we are allowed to
+// perform during a single frame and the time spent rasterizing.
+// TODO(skyostil): Determine these limits more dynamically.
+const int kMaxCheapRasterCount = 6;
+const int kMaxCheapRasterMilliseconds = 6;
+
 void didVisibilityChange(cc::LayerTreeHostImpl* id, bool visible)
 {
     if (visible) {
@@ -159,6 +165,7 @@ LayerTreeHostImpl::LayerTreeHostImpl(const LayerTreeSettings& settings, LayerTre
     , m_lastSentMemoryVisibleAndNearbyBytes(0)
     , m_lastSentMemoryUseBytes(0)
     , m_animationRegistrar(AnimationRegistrar::create())
+    , m_cheapRasterCount(0)
 {
     DCHECK(m_proxy->isImplThread());
     didVisibilityChange(this, m_visible);
@@ -715,6 +722,28 @@ void LayerTreeHostImpl::DidUploadVisibleHighResolutionTile()
         m_client->didUploadVisibleHighResolutionTileOnImplThread();
 }
 
+bool LayerTreeHostImpl::CanDoAnotherCheapRaster() const
+{
+    DCHECK(m_settings.useCheapnessEstimator);
+    if (m_cheapRasterCount >= kMaxCheapRasterCount) {
+        TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::CanDoAnotherCheapRaster did too many");
+        return false;
+    }
+    if (m_cheapRasterDeadline.is_null() || base::TimeTicks::Now() >= m_cheapRasterDeadline) {
+        TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::CanDoAnotherCheapRaster out of time");
+        m_cheapRasterDeadline = base::TimeTicks();
+        return false;
+    }
+    return true;
+}
+
+void LayerTreeHostImpl::DidPerformCheapRaster()
+{
+    DCHECK(m_settings.useCheapnessEstimator);
+    m_cheapRasterCount++;
+    DCHECK(m_cheapRasterCount <= kMaxCheapRasterCount);
+}
+
 bool LayerTreeHostImpl::shouldClearRootRenderPass() const
 {
     return m_settings.shouldClearRootRenderPass;
@@ -847,6 +876,10 @@ const RendererCapabilities& LayerTreeHostImpl::rendererCapabilities() const
 
 bool LayerTreeHostImpl::swapBuffers()
 {
+    if (m_settings.useCheapnessEstimator) {
+        m_cheapRasterCount = 0;
+        m_cheapRasterDeadline = base::TimeTicks::Now() + base::TimeDelta::FromMilliseconds(kMaxCheapRasterMilliseconds);
+    }
     return m_renderer->swapBuffers();
 }