RRO: prevent duplicate system overlays

System overlays, ie overlays with targetPackage="android", were loaded
twice, which caused all sorts of issues. Ensure they are only loaded
once, which will be during Zygote initialization.

Bug: 17765434
Change-Id: Ia5064045c77f713c58fb78adc3942f6af1abdc93

include/androidfw/AssetManager.h

@@ -236,9 +236,11 @@ public:
 private:
     struct asset_path
     {
+        asset_path() : path(""), type(kFileTypeRegular), idmap(""), isSystemOverlay(false) {}
         String8 path;
         FileType type;
         String8 idmap;
+        bool isSystemOverlay;
     };
 
     Asset* openInPathLocked(const char* fileName, AccessMode mode,

libs/androidfw/AssetManager.cpp

@@ -605,6 +605,11 @@ FileType AssetManager::getFileType(const char* fileName)
 }
 
 bool AssetManager::appendPathToResTable(const asset_path& ap) const {
+    // skip those ap's that correspond to system overlays
+    if (ap.isSystemOverlay) {
+        return true;
+    }
+
     Asset* ass = NULL;
     ResTable* sharedRes = NULL;
     bool shared = true;
@@ -790,6 +795,7 @@ void AssetManager::addSystemOverlays(const char* pathOverlaysList,
         oap.path = String8(buf, space - buf);
         oap.type = kFileTypeRegular;
         oap.idmap = String8(space + 1, newline - space - 1);
+        oap.isSystemOverlay = true;
 
         Asset* oass = const_cast<AssetManager*>(this)->
             openNonAssetInPathLocked("resources.arsc",