Change the scale factor of texture_size from the layer's one to an estimation.

ui/compositor/layer.cc

Index: ui/compositor/layer.cc
diff --git a/ui/compositor/layer.cc b/ui/compositor/layer.cc
index 7e7964900876cb70a32b835c53a83ef05d51e087..39c1ff47dede7f83d4649f95b4a54da3c8a8d5a4 100644
--- a/ui/compositor/layer.cc
+++ b/ui/compositor/layer.cc
@@ -65,7 +65,8 @@ Layer::Layer()
       delegate_(NULL),
       web_layer_(NULL),
       scale_content_(true),
-      device_scale_factor_(1.0f) {
+      device_scale_factor_(1.0f),
+      device_scale_factor_for_texture_(1.0f) {
   CreateWebLayer();
 }
 
@@ -87,7 +88,8 @@ Layer::Layer(LayerType type)
       layer_mask_back_link_(NULL),
       delegate_(NULL),
       scale_content_(true),
-      device_scale_factor_(1.0f) {
+      device_scale_factor_(1.0f),
+      device_scale_factor_for_texture_(1.0f) {
   CreateWebLayer();
 }
 
@@ -378,6 +380,7 @@ void Layer::SetExternalTexture(Texture* texture) {
   DCHECK_EQ(type_, LAYER_TEXTURED);
   layer_updated_externally_ = !!texture;
   texture_ = texture;
+  device_scale_factor_for_texture_ = device_scale_factor_;

[piman, 2012/09/20 23:20:07]

mmh, that may solve the problem in a given case, but not the general problem.
If you have one layer tree that's on screen1 with a device ratio R1, and one
layer tree that's on screen2 with device ratio R2, and you want to put the same
texture in both, this won't work.
What you really want is to have a per-texture device pixel ratio. There's no
reason we can't extend Texture for that - and they're only created in 2 places,
both in ImageTransportFactory, only called from RenderWidgetHostViewAura, which
incidentally is what knows the pixel ratio for the texture.

[Jun Mukai, 2012/09/21 00:53:55]

hmm, then added the device_scale_factor to ui::Texture itself.  please take
another look, again.

   if (web_layer_is_accelerated_ != layer_updated_externally_) {
     // Switch to a different type of layer.
     web_layer_->removeAllChildren();
@@ -749,10 +752,12 @@ void Layer::RecomputeDrawsContentAndUVRect() {
     DCHECK(texture_);
 
     gfx::Size texture_size;
-    if (scale_content_)
+    if (scale_content_) {
       texture_size = texture_->size();
-    else
-      texture_size = ConvertSizeToDIP(this, texture_->size());
+    } else {
+      texture_size =
+          texture_->size().Scale(1.0f / device_scale_factor_for_texture_);
+    }
 
     gfx::Size size(std::min(bounds().width(), texture_size.width()),
                    std::min(bounds().height(), texture_size.height()));