Add ResourceLoader API with .apk and .arsc support

ResourceLoaders allow inserting another .apk/.arsc into AssetManager's
resource resolution search. The effect is similar to overlays,
where a entry of >= config later in the path list will return that
ApkAsset's resource value instead.

Because loading from an .arsc is supported, which doesn't contain
any actual files, ResourceLoader exposes loadDrawable and
loadXmlResourceParser to allow an application load those files from
anywhere or create them in code.

The data being loaded is either pushed into an .apk or .arsc that
mocks itself as the package being "overlaid" and is passed in
through ResourcesProvider, an interface with static methods that
supports loading from a readable path on disk or a FileDescriptor.

The APIs are accessed through a Context's getResources(), which
has been changed to be unique per "Context-scope", which is usually
the lifetime of the Java object. The exception is that Activities
who get their Resources object persisted across recreations
maintain that logic for persisting ResourceLoaders.

Bug: 135270223

Test: atest FrameworksResourceLoaderTests

Change-Id: I6929f0828629ad39a21fa155e7fec73bd75eec7d

1 files changed, 15 insertions, 5 deletions

diff --git a/libs/androidfw/Asset.cpp b/libs/androidfw/Asset.cpp
index 92125c9da8bb..c132f343713f 100644
--- a/libs/androidfw/Asset.cpp
+++ b/libs/androidfw/Asset.cpp
@@ -133,14 +133,24 @@ Asset::Asset(void)
  */
 /*static*/ Asset* Asset::createFromFile(const char* fileName, AccessMode mode)
 {
+    return createFromFd(open(fileName, O_RDONLY | O_BINARY), fileName, mode);
+}
+
+/*
+ * Create a new Asset from a file on disk.  There is a fair chance that
+ * the file doesn't actually exist.
+ *
+ * We can use "mode" to decide how we want to go about it.
+ */
+/*static*/ Asset* Asset::createFromFd(const int fd, const char* fileName, AccessMode mode)
+{
+    if (fd < 0) {
+        return NULL;
+    }
+
     _FileAsset* pAsset;
     status_t result;
     off64_t length;
-    int fd;
-
-    fd = open(fileName, O_RDONLY | O_BINARY);
-    if (fd < 0)
-        return NULL;
 
     /*
      * Under Linux, the lseek fails if we actually opened a directory.  To