Introduce painted-device-scale-factor and use it when --enable-use-zoom-for-dsf is specified.

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 47c4ee003382c99d34786c6441bfd0deeabbe4fb..0449b390c3fdeb2c66f84c06ce362664f0356532 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -58,6 +58,7 @@ LayerTreeImpl::LayerTreeImpl(
       min_page_scale_factor_(0),
       max_page_scale_factor_(0),
       device_scale_factor_(1.f),
+      painted_device_scale_factor_(0.f),
       elastic_overscroll_(elastic_overscroll),
       viewport_size_invalid_(false),
       needs_update_draw_properties_(true),
@@ -315,6 +316,7 @@ void LayerTreeImpl::PushPropertiesTo(LayerTreeImpl* target_tree) {
   target_tree->PushPageScaleFactorAndLimits(nullptr, min_page_scale_factor(),
                                             max_page_scale_factor());
   target_tree->SetDeviceScaleFactor(device_scale_factor());
+  target_tree->SetPaintedDeviceScaleFactor(painted_device_scale_factor());
   target_tree->elastic_overscroll()->PushPendingToActive();
 
   target_tree->pending_page_scale_animation_ =
@@ -525,6 +527,16 @@ void LayerTreeImpl::SetDeviceScaleFactor(float device_scale_factor) {
     layer_tree_host_impl_->SetFullRootLayerDamage();
 }
 
+void LayerTreeImpl::SetPaintedDeviceScaleFactor(
+    float painted_device_scale_factor) {
+  if (painted_device_scale_factor == painted_device_scale_factor_)
+    return;
+  painted_device_scale_factor_ = painted_device_scale_factor;
+
+  if (IsActiveTree())
+    layer_tree_host_impl_->SetFullRootLayerDamage();

[danakj, 2015/10/22 23:15:29]

i don't think this is needed, we'll get invalidations from blink if its scale
factor changed and it repainted things

so you could make this simply set_painted_de..sc..factor() in the header file?

[oshima, 2015/10/23 18:05:36]

Done.

+}
+
 SyncedProperty<ScaleGroup>* LayerTreeImpl::page_scale_factor() {
   return page_scale_factor_.get();
 }