Refactor base's proguard flags to be more usable by cronet

base/android/release_proguard_config.flags

-# Allows Proguard freedom in removing these log related calls. We ask for debug
-# and verbose logs to be stripped out in base.Log, so we are just ensuring we
-# get rid of all other debug/verbose logs.
--assumenosideeffects class android.util.Log {
-  static *** d(...);
-  static *** v(...);
-  static *** isLoggable(...);
-}
-
-# The following chart was created on July 20, 2016, to decide on 3 optimization
-# passes for Chrome.
-# optimization passes | time | .dex size | dirty memory per process
-# -----------------------------------------------------------------
-#          1          | 0:48 |  5805676  |         488972
-#          2          | 1:07 |  5777376  |         487092
-#          3          | 1:24 |  5772192  |         486596
-#          4          | 1:42 |  5771124  |         486484
-#          5          | 1:56 |  5770504  |         486432
--optimizationpasses 3
-
-# Class merging messes up stacktraces beyond the point of them being
-# deobfuscatable. If turned on, it would give us a 2% reduction in .dex size.
--optimizations !class/merging/*
-
-# Allowing Proguard to change modifiers. This change shrinks the .dex size by
-# ~1%, and reduces the method count by ~4%.
--allowaccessmodification
-
-# The support library contains references to newer platform versions.
-# Don't warn about those in case this app is linking against an older
-# platform version.  We know about them, and they are safe.
--dontwarn android.support.**