Enforce READ_DROPBOX_DATA permission for ecall diagnostics.

Following privacy review done for the recent mainline changes to resolve
TelephonyManager#persistEmergencyCallDiagnosticData, ensure that
READ_DROPBOX_DATA is explicitly required. Since the new changes have
been gated by a flag, this permission check needs to be conditionally
checked on the same premise.

Bug: 328132903
Test: Manual
Test: atest TelephonyManagerTest
Change-Id: Ibd75727aaa7a40f23b44ed20dceaeb18c1146100
diff --git a/Android.bp b/Android.bp
index c717d86..3bbafc0 100644
--- a/Android.bp
+++ b/Android.bp
@@ -49,6 +49,7 @@
         "android.permission.flags-aconfig-java",
         "satellite-s2storage-ro",
         "s2-geometry-library-java",
+        "dropbox_flags_lib",
     ],
 
     srcs: [