Moving flags out of base_proguard_config make it usable by other .apks

chrome/android/java/proguard.flags

 # 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
+
 # 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
 
 # Keep protobuf code used via reflection
 # TODO(tonyg): Removing these -keeps results in new notes, but nothing seems to
 # break. This exclusion costs almost 100k of dex size so consider replacing it
 # with a -dontnote after more testing.
 -keep class com.google.protobuf.** {
@@ skipping 26 matching lines @@
 # 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.**
 
 # Proguard mistakenly optimizes away some null checks on final fields
 # in the support library.
 # See https://sourceforge.net/p/proguard/bugs/531/#fdc9/41e2
 -keepclassmembers,allowshrinking,allowobfuscation class android.support.v7.widget.AppCompatButton {
   !static final <fields>;
 }