drm_hwcomposer: Use vector for overlay planes

For two reasons:
1- Because we don't need to use deque
2- Because we'll need to erase from the middle in the future,
   and deque makes that difficult while iterating

BUG=chrome-os-parter:42311
TEST=Tested on smaug, turned on/off bunch of times, no dup icons

Change-Id: I306bdea15d7165f63afeb3b1e06774e2e9a1785f
Signed-off-by: Sean Paul <seanpaul@chromium.org>
diff --git a/drmcomposition.h b/drmcomposition.h
index e490811..902d7c7 100644
--- a/drmcomposition.h
+++ b/drmcomposition.h
@@ -52,7 +52,7 @@
   Importer *importer_;
 
   std::vector<DrmPlane *> primary_planes_;
-  std::deque<DrmPlane *> overlay_planes_;
+  std::vector<DrmPlane *> overlay_planes_;
 
   /*
    * This _must_ be read-only after it's passed to QueueComposition. Otherwise