Preload public native libraries

Preload libraries needed by the public namespace
at the earlier stage. This saves time on
InitPublicNamespace and saves memory because
the libraries are linked before zygote fork.

Bug: http://b/26409579
Change-Id: I59153a4180b930f31b542d8d2cb17b5d63c36774
diff --git a/libnativeloader/native_loader.cpp b/libnativeloader/native_loader.cpp
index 75d2a2d..aaff64c 100644
--- a/libnativeloader/native_loader.cpp
+++ b/libnativeloader/native_loader.cpp
@@ -62,7 +62,9 @@
 
 class LibraryNamespaces {
  public:
-  LibraryNamespaces() : initialized_(false) { }
+  LibraryNamespaces() : initialized_(false) {
+    PreloadPublicLibraries();
+  }
 
   android_namespace_t* GetOrCreate(JNIEnv* env, jobject class_loader,
                                    bool is_shared,
@@ -108,15 +110,16 @@
   }
 
  private:
-  bool InitPublicNamespace(const char* library_path) {
-    // Make sure all the public libraries are loaded
+  void PreloadPublicLibraries() {
+    // android_init_namespaces() expects all the public libraries
+    // to be loaded so that they can be found by soname alone.
     std::vector<std::string> sonames = android::base::Split(kPublicNativeLibraries, ":");
     for (const auto& soname : sonames) {
-      if (dlopen(soname.c_str(), RTLD_NOW | RTLD_NODELETE) == nullptr) {
-        return false;
-      }
+      dlopen(soname.c_str(), RTLD_NOW | RTLD_NODELETE);
     }
+  }
 
+  bool InitPublicNamespace(const char* library_path) {
     // Some apps call dlopen from generated code unknown to linker in which
     // case linker uses anonymous namespace. See b/25844435 for details.
     initialized_ = android_init_namespaces(kPublicNativeLibraries, library_path);