Add API for custom library loading

components/cronet/android/api/src/org/chromium/net/CronetEngine.java

Index: components/cronet/android/api/src/org/chromium/net/CronetEngine.java
diff --git a/components/cronet/android/api/src/org/chromium/net/CronetEngine.java b/components/cronet/android/api/src/org/chromium/net/CronetEngine.java
index 6336533491fe1c048429edb41211dcd51e33b7d6..9f2f7b7ab3180c015e213808f13e7ad6068efdae 100644
--- a/components/cronet/android/api/src/org/chromium/net/CronetEngine.java
+++ b/components/cronet/android/api/src/org/chromium/net/CronetEngine.java
@@ -41,6 +41,19 @@ public abstract class CronetEngine {
      * then {@link #build} is called to create the {@code CronetEngine}.
      */
     public static class Builder {
+        /**
+         * A callback for loading the "cronet" library.

[xunjieli, 2016/01/21 19:50:53]

Suggest making this into an abstract class, and mLibraryLoader as an optional
param.
Maybe also rename LibraryLoader to CustomLibraryLoader.

That way we can avoid creating an instance of LibraryLoader if it isn't needed.
It is slightly clearer that this step is optional.

Also document in what scenarios the embedder might want to have a custom
LibraryLoader. A few sentences will do.

[mgersh, 2016/01/22 17:41:16]

I made it into an interface instead, since it looks like it meets all the
criteria for that. Let me know if there's a reason for it to be specifically an
abstract class.

+         */
+        public static class LibraryLoader {
+            /**
+             * Load the native library.
+             */
+            public void loadLibrary(Context context, String name) {

[xunjieli, 2016/01/21 19:50:53]

I don't think we need the context as an argument. If the embedder needs it, they
can have it through other means e.g. supplied through the constructor.

Also document what "name" is. Maybe rename it to libName to be clearer.

[mgersh, 2016/01/22 17:41:16]

Done.

+                // The context isn't used here, but other implementations might need it
+                System.loadLibrary(name);
+            }
+        }
+
         // A hint that a host supports QUIC.
         static class QuicHint {
             // The host.
@@ -86,6 +99,7 @@ public abstract class CronetEngine {
         private String mUserAgent;
         private String mStoragePath;
         private boolean mLegacyModeEnabled;
+        private LibraryLoader mLibraryLoader;
         private String mLibraryName;
         private boolean mQuicEnabled;
         private boolean mHttp2Enabled;
@@ -107,6 +121,7 @@ public abstract class CronetEngine {
         public Builder(Context context) {
             mContext = context;
             setLibraryName("cronet");
+            setLibraryLoader(new LibraryLoader());
             enableLegacyMode(false);
             enableQUIC(false);
             enableHTTP2(true);
@@ -187,8 +202,17 @@ public abstract class CronetEngine {
             return this;
         }
 
-        String libraryName() {
-            return mLibraryName;
+        /**
+         * Overrides the callback to load the native library.
+         * @return the builder to facilitate chaining.
+         */
+        public Builder setLibraryLoader(LibraryLoader loader) {
+            mLibraryLoader = loader;
+            return this;
+        }
+
+        void loadLibrary(Context context) {
+            mLibraryLoader.loadLibrary(context, mLibraryName);

[xunjieli, 2016/01/21 19:50:53]

Suggest do the following:
If mLibraryLoader is null, do System.loadLibrary( mLibraryName);
Otherwise invoke the loadLibrary on mLibraryLoader.

[mgersh, 2016/01/22 17:41:16]

Done.

         }
 
         /**