drm_hwcomposer: implement the safe handling of layers

This is a sweeping change to discard our usage of struct hwc_layer_t outside
hwcomposer.cpp. That was a dangerous struct that was a source of many of our
errors. Replacing it with safer RAII-style classes reduces the amount and
complexity of our code.

Change-Id: I580cafdf89bd1e7e6583f3073858b8e78e6018ba
diff --git a/drmcomposition.h b/drmcomposition.h
index 426ced0..a5d9cf1 100644
--- a/drmcomposition.h
+++ b/drmcomposition.h
@@ -22,7 +22,6 @@
 #include "drmplane.h"
 #include "importer.h"
 
-#include <deque>
 #include <map>
 #include <vector>
 
@@ -33,9 +32,11 @@
 
 struct DrmCompositionDisplayLayersMap {
   int display;
-  size_t num_layers;
-  hwc_layer_1_t *layers;
-  size_t *layer_indices;
+  std::vector<DrmHwcLayer> layers;
+
+  DrmCompositionDisplayLayersMap() = default;
+  DrmCompositionDisplayLayersMap(DrmCompositionDisplayLayersMap &&rhs) =
+      default;
 };
 
 class DrmComposition {
@@ -44,8 +45,7 @@
 
   int Init(uint64_t frame_no);
 
-  int SetLayers(size_t num_displays,
-                const DrmCompositionDisplayLayersMap *maps);
+  int SetLayers(size_t num_displays, DrmCompositionDisplayLayersMap *maps);
   int SetDpmsMode(int display, uint32_t dpms_mode);
 
   std::unique_ptr<DrmDisplayComposition> TakeDisplayComposition(int display);