Make exo::Surface set device_scale_factor.

exo::Surface wasn't setting the device_scale_factor in CompositorFrames.
This was triggering a DCHECK when the SurfaceInfo for new cc::Surfaces
have device_scale_factor == 0.

BUG=b/37654593

Review-Url: https://codereview.chromium.org/2843723003
Cr-Commit-Position: refs/heads/master@{#468076}

components/exo/surface.cc

@@ -108,7 +108,9 @@ class CustomWindowDelegate : public aura::WindowDelegate {
   bool CanFocus() override { return true; }
   void OnCaptureLost() override {}
   void OnPaint(const ui::PaintContext& context) override {}
-  void OnDeviceScaleFactorChanged(float device_scale_factor) override {}
+  void OnDeviceScaleFactorChanged(float device_scale_factor) override {
+    surface_->SetDeviceScaleFactor(device_scale_factor);
+  }
   void OnWindowDestroying(aura::Window* window) override {}
   void OnWindowDestroyed(aura::Window* window) override { delete this; }
   void OnWindowTargetVisibilityChanged(bool visible) override {}
@@ -405,6 +407,10 @@ void Surface::SetAlpha(float alpha) {
   pending_state_.alpha = alpha;
 }
 
+void Surface::SetDeviceScaleFactor(float device_scale_factor) {
+  device_scale_factor_ = device_scale_factor;
+}
+
 void Surface::Commit() {
   TRACE_EVENT0("exo", "Surface::Commit");
 
@@ -847,6 +853,7 @@ void Surface::UpdateSurface(bool full_damage) {
     current_begin_frame_ack_.has_damage = true;
   }
   frame.metadata.begin_frame_ack = current_begin_frame_ack_;
+  frame.metadata.device_scale_factor = device_scale_factor_;
 
   if (current_resource_.id) {
     // Texture quad is only needed if buffer is not fully transparent.

components/exo/surface.h

@@ -140,6 +140,9 @@ class Surface : public ui::ContextFactoryObserver,
   // This sets the alpha value that will be applied to the whole surface.
   void SetAlpha(float alpha);
 
+  // This sets the device scale factor sent in CompositorFrames.
+  void SetDeviceScaleFactor(float device_scale_factor);
+
   // Surface state (damage regions, attached buffers, etc.) is double-buffered.
   // A Commit() call atomically applies all pending state, replacing the
   // current state. Commit() is not guaranteed to be synchronous. See
@@ -314,6 +317,9 @@ class Surface : public ui::ContextFactoryObserver,
   // The buffer that will become the content of surface when Commit() is called.
   BufferAttachment pending_buffer_;
 
+  // The device scale factor sent in CompositorFrames.
+  float device_scale_factor_ = 1.0f;
+
   const cc::FrameSinkId frame_sink_id_;
   cc::LocalSurfaceId local_surface_id_;