Add the partial screen magnifier to Chrome OS.

ui/compositor/layer.cc

Index: ui/compositor/layer.cc
diff --git a/ui/compositor/layer.cc b/ui/compositor/layer.cc
index 67d4ca7e90abbf4ea78c6fa3be5f0c66d94f0339..d8e130f26a692f21af1b907a83059da7bd8d616a 100644
--- a/ui/compositor/layer.cc
+++ b/ui/compositor/layer.cc
@@ -60,6 +60,9 @@ Layer::Layer()
       layer_inverted_(false),
       layer_mask_(NULL),
       layer_mask_back_link_(NULL),
+      zoom_x_offset_(0),
+      zoom_y_offset_(0),
+      zoom_(1),
       delegate_(NULL),
       web_layer_(NULL),
       scale_content_(true),
@@ -83,6 +86,9 @@ Layer::Layer(LayerType type)
       layer_inverted_(false),
       layer_mask_(NULL),
       layer_mask_back_link_(NULL),
+      zoom_x_offset_(0),
+      zoom_y_offset_(0),
+      zoom_(1),
       delegate_(NULL),
       scale_content_(true),
       device_scale_factor_(1.0f) {
@@ -294,6 +300,21 @@ void Layer::SetMaskLayer(Layer* layer_mask) {
     layer_mask->layer_mask_back_link_ = this;
 }
 
+void Layer::SetBackgroundZoom(float x_offset, float y_offset, float zoom) {
+  zoom_x_offset_ = x_offset;

[sky, 2012/09/07 16:06:59]

These values aren't used locally, only passed to webkit. Why do we need to cache
them in Layer too?

[Zachary Kuznia, 2012/09/13 11:49:02]

Done.

+  zoom_y_offset_ = y_offset;
+  zoom_ = zoom;
+
+  WebKit::WebFilterOperations filters;
+  if (zoom_ != 1) {
+    filters.append(WebKit::WebFilterOperation::createZoomFilter(
+        WebKit::WebRect(zoom_x_offset_, zoom_y_offset_,
+                        (bounds().width() / zoom_),

[piman, 2012/09/07 21:38:56]

is bounds() what you want, if the layer is animated? It feels like
GetTargetBounds() would be more appropriate.

[Zachary Kuznia, 2012/09/13 11:49:02]

Done.

+                        (bounds().height() / zoom_)), 16));

[piman, 2012/09/07 21:38:56]

16 looks very magic. Should it be passed as a parameter to SetBackgroundZoom?

[Zachary Kuznia, 2012/09/13 11:49:02]

Done.

+  }
+  web_layer_->setBackgroundFilters(filters);

[piman, 2012/09/07 21:38:56]

This overrides the SetBackgroundBlur setting and vice versa. Can we make sure to
keep this orthogonal? E.g. by recreating the background filter list when either
of them changes.

[Zachary Kuznia, 2012/09/13 11:49:02]

Done.

+}
+
 void Layer::SetLayerFilters() {
   WebKit::WebFilterOperations filters;
   if (layer_saturation_) {