bind/java: reenable asset access.

This is done by moving app.Context to internal/mobileinit,
introducing mobileinit.SetCurrentContext and,
making bind/java depend on it.

TODO: check gomobile bind's proguard rule - context lookup
was implemented through reflection on android.app.AppGlobals class.

Change-Id: Ieb6ad503eeef8c2c1c5836a21c667938c5a701a2
Reviewed-on: https://go-review.googlesource.com/12279
Reviewed-by: David Crawshaw <crawshaw@golang.org>

bind/java/Seq.java

@@ -4,6 +4,8 @@
 
 package go;
 
+import android.app.Application;
+import android.content.Context;
 import android.util.Log;
 import android.util.SparseArray;
 import android.util.SparseIntArray;
@@ -24,6 +26,16 @@ public class Seq {
 			Log.w("GoSeq", "LoadJNI class not found");
 		}
 
+		try {
+			// TODO(hyangah): check proguard rule.
+			Application appl = (Application)Class.forName("android.app.AppGlobals").getMethod("getInitialApplication").invoke(null, (Object[]) null);
+			Context ctx = appl.getApplicationContext();
+			setContext(ctx);
+
+		} catch (Exception e) {
+			Log.w("GoSeq", "Global context not found:" + e);
+		}
+
 		initSeq();
 		new Thread("GoSeq") {
 			public void run() { Seq.receive(); }
@@ -37,6 +49,8 @@ public class Seq {
 		ensure(64);
 	}
 
+	static native void setContext(Context ctx);
+
 	// Ensure that at least size bytes can be written to the Seq.
 	// Any existing data in the buffer is preserved.
 	public native void ensure(int size);