cc: Ensure that raster contents scale doesn't go below min scale.

This patch ensures that we can the raster scale to min contents scale.
We already did this, but later could modify the value again to be lower
than MinContentsScale. Now, the clamp happens near the end of the
function.

R=danakj
BUG=429397

Review URL: https://codereview.chromium.org/699053003

Cr-Commit-Position: refs/heads/master@{#302636}

cc/layers/picture_layer_impl.cc

@@ -1087,9 +1087,6 @@ void PictureLayerImpl::RecalculateRasterScales() {
         raster_contents_scale_ / raster_device_scale_ / raster_source_scale_;
   }
 
-  raster_contents_scale_ =
-      std::max(raster_contents_scale_, MinimumContentsScale());
-
   // If we're not re-rasterizing during animation, rasterize at the maximum
   // scale that will occur during the animation, if the maximum scale is
   // known. However we want to avoid excessive memory use. If the scale is
@@ -1121,6 +1118,9 @@ void PictureLayerImpl::RecalculateRasterScales() {
       raster_contents_scale_ = 1.f * ideal_page_scale_ * ideal_device_scale_;
   }
 
+  raster_contents_scale_ =
+      std::max(raster_contents_scale_, MinimumContentsScale());
+
   // If this layer would create zero or one tiles at this content scale,
   // don't create a low res tiling.
   gfx::Size raster_bounds = gfx::ToCeiledSize(
@@ -1138,6 +1138,8 @@ void PictureLayerImpl::RecalculateRasterScales() {
   low_res_raster_contents_scale_ = std::max(
       raster_contents_scale_ * low_res_factor,
       MinimumContentsScale());
+  DCHECK_LE(low_res_raster_contents_scale_, raster_contents_scale_);
+  DCHECK_GE(low_res_raster_contents_scale_, MinimumContentsScale());
 }
 
 void PictureLayerImpl::CleanUpTilingsOnActiveLayer(