Add bootclasspath_fragment.

Note that the contents of the bootclasspath_fragment are added as
dependencies to an apex, so there is no need to duplicate them in
java_libs.

Bug: 180105615
Test: atest CtsClasspathsTestCases
Change-Id: Ic80a004135d2747472f98d6c7e666c4acb14badf
diff --git a/apex/Android.bp b/apex/Android.bp
index a5e9942..cb6da5f 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -17,7 +17,7 @@
 
 apex_defaults {
     name: "com.android.mediaprovider-defaults",
-    java_libs: ["framework-mediaprovider"],
+    bootclasspath_fragments: ["com.android.mediaprovider-bootclasspath-fragment"],
     key: "com.android.mediaprovider.key",
     certificate: ":com.android.mediaprovider.certificate",
     file_contexts: ":com.android.mediaprovider-file_contexts",
@@ -45,3 +45,10 @@
         "framework-mediaprovider",
     ],
 }
+
+// Encapsulate the contributions made by the com.android.mediaprovider to the bootclasspath.
+bootclasspath_fragment {
+    name: "com.android.mediaprovider-bootclasspath-fragment",
+    contents: ["framework-mediaprovider"],
+    apex_available: ["com.android.mediaprovider"],
+}