Adding new shared config for Chrome and WebView

chrome/android/java/proguard.flags

 # As of August 11, 2016, obfuscation was tested and passed on the trybots,
 # saving us 660kb on our .dex size and 53kb memory/process. Enable obfuscation
 # as soon as Crash supports ReTrace's deobfuscation of stack traces.
 #
 # To enable obfuscation, remove the -keepnames rule for
 # com.google.android.apps.chrome.** and org.chromium.**, and uncomment the
 # following two lines:
 # -renamesourcefileattribute PG
 # -repackageclasses ""
 
 # Disable obfuscation for the following two packages.
 -keepnames,allowoptimization class com.google.android.apps.chrome.**,org.chromium.** {
   *;
 }
 
-# The following chart was created on July 20, 2016, to decide on 3 optimization
-# passes.
-# 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
-# ~1.1%, and reduces the method count by ~4.3%.
--allowaccessmodification
-
-# 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(...);
-}
-
 # Fragments are loaded using reflection via Fragment.instantiate(Context,String)
 # This can be improved upon - see crbug.com/622023.
 -keep public class com.google.android.apps.chrome** extends android.app.Fragment
 -keep public class org.chromium** extends android.app.Fragment
 
 # These classes aren't themselves referenced, but __ProcessService[0,1,2...] are
 # referenced, and we look up these services by appending a number onto the name
 # of the base class. Thus, we need to keep the base class name around so that
 # the child classes can be looked up.
 -keep class org.chromium.content.app.SandboxedProcessService
 -keep class org.chromium.content.app.PrivilegedProcessService
 
 # Keep all Parcelables as they might be marshalled outside Chrome.
 -keepnames class * implements android.os.Parcelable {
    public static final ** CREATOR;
 }
 
 # SearchView is used in website_preferences_menu.xml and is constructed by
 # Android using reflection.
 -keep class android.support.v7.widget.SearchView {
   public <init>(...);
 }
 
 # Google Play Services warnings are about its resources.
 -dontwarn com.google.android.gms.R**
-
-# 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.**