Store layers with pending frames as smart pointers instead of raw pointers

Layers can be removed in between invalidations, which is problematic
when using raw pointers. Instead, store a set of sp<Layer> with a custom
hash

Bug: 170729573
Test: builds
Change-Id: I87dd48a7767b8c05461cb4e56b3fbcd037d0603e
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 576bd50..f8260c3 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -2110,7 +2110,7 @@
     ALOGV("postComposition");
 
     nsecs_t dequeueReadyTime = systemTime();
-    for (auto layer : mLayersWithQueuedFrames) {
+    for (const auto& layer : mLayersWithQueuedFrames) {
         layer->releasePendingBuffer(dequeueReadyTime);
     }
 
@@ -3055,7 +3055,7 @@
         // writes to Layer current state. See also b/119481871
         Mutex::Autolock lock(mStateLock);
 
-        for (auto& layer : mLayersWithQueuedFrames) {
+        for (const auto& layer : mLayersWithQueuedFrames) {
             if (layer->latchBuffer(visibleRegions, latchTime, expectedPresentTime)) {
                 mLayersPendingRefresh.push_back(layer);
             }