drm_hwcomposer: Deprecate usage of HWC2 GetActiveConfig

Add HwcDisplay::GetLastRequestedConfig, and use this to implement
support for getActiveConfig.

Change-Id: I089e2ac0046eceb5da9c130537105290a973ae4a
Signed-off-by: Drew Davenport <ddavenport@google.com>
diff --git a/hwc2_device/HwcDisplay.h b/hwc2_device/HwcDisplay.h
index 7cdc0b8..a315540 100644
--- a/hwc2_device/HwcDisplay.h
+++ b/hwc2_device/HwcDisplay.h
@@ -62,6 +62,11 @@
   // Get the config representing the mode that has been committed to KMS.
   const HwcDisplayConfig *GetCurrentConfig() const;
 
+  // Get the config that was last requested through SetActiveConfig and similar
+  // functions. This may differ from the GetCurrentConfig if the config change
+  // is queued up to take effect in the future.
+  const HwcDisplayConfig *GetLastRequestedConfig() const;
+
   // HWC2 Hooks - these should not be used outside of the hwc2 device.
   HWC2::Error AcceptDisplayChanges();
   HWC2::Error CreateLayer(hwc2_layer_t *layer);