[Cronet] add base proguard flags

components/cronet/android/proguard.cfg

Index: components/cronet/android/proguard.cfg
diff --git a/components/cronet/android/proguard.cfg b/components/cronet/android/proguard.cfg
index 853747da727ba837b7ba46d15954389f0584a4a1..3281ebc02325683ded6cbb1916bbefd253d8f0e3 100644
--- a/components/cronet/android/proguard.cfg
+++ b/components/cronet/android/proguard.cfg
@@ -1,35 +1,9 @@
-# Keep annotations used by chromium to keep members referenced by native code
--keep class org.chromium.base.annotations.*Native*
--keep class org.chromium.base.annotations.JNINamespace
--keepclasseswithmembers class org.chromium.** {
-    @org.chromium.base.annotations.AccessedByNative <fields>;
-}
--keepclasseswithmembers class org.chromium.** {
-    @org.chromium.base.annotations.*Native* <methods>;
-}
-
-# TODO(mef) remove unnecessary classes from base, so we don't have to preserve
-# their methods
--keepclasseswithmembers class org.chromium.** {
-    native <methods>;
-}
-
-# TODO(xunjieli): Find an alternative to explictly preserving public classes.
--keep public class org.chromium.net.*
-
 -keep class org.chromium.net.impl.CronetUrlRequest$HeadersList
 -keep class org.chromium.net.impl.ChromiumUrlRequest$ResponseHeadersMap
 
 # Needed so that multiple optimization passes will detect annotations
 -keepattributes *Annotation*

[smaier, 2016/08/11 16:08:29]

I'd wager you'll be able to remove this line. base_proguard_config already
contains the following lines:

-keepattributes RuntimeVisible*Annotations
-keepattributes AnnotationDefault

Effectively, what this means is that your config will additionally keep
RuntimeInvisibleParameterAnnotations, RuntimeInvisibleAnnotations, and
RuntimeInvisibleTypeAnnotations on top of what's already kept in base. From my
experience, none of these will affect multiple optimization passes.

What they will affect, are any tools looking for these compile-time-only
annotations in the ProGuarded .class files. Perhaps you still want to keep
around compile-time annotations after ProGuard, and if so, ignore this comment.

[xunjieli, 2016/08/11 21:05:53]

Done. Thanks for pointing that out and explaining the significance of these
annotations! That makes sense. We don't have these annotations, so I think the
original line was added to deal with base. Since it is already handled by
base_proguard_config, I think we can do without this line. 

 
-# Keep methods used by reflection
--keep class org.chromium.base.annotations.UsedByReflection
--keep @org.chromium.base.annotations.UsedByReflection class *
--keepclassmembers class * {
-    @org.chromium.base.annotations.UsedByReflection *;
-}
-
 # Suppress unnecessary warnings.
 -dontnote org.chromium.net.ProxyChangeListener$ProxyReceiver
 -dontnote org.chromium.net.AndroidKeyStore