Android: Add -shrinkunusedprotofields proguard flag

And removes some obsolete flags

Change-Id: Ia51b586f00c0c9eeb30d588f20f0743af5b2e395
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2169755
Commit-Queue: Sam Maier <smaier@chromium.org>
Auto-Submit: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Sam Maier <smaier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#763423}

base/android/proguard/chromium_apk.flags

@@ -4,12 +4,15 @@
 
 # Contains flags that we'd like all Chromium .apks to use.
 
-# Not needed for Android and saves a bit of processing time.
--dontpreverify
-
 # Keep line number information, useful for stack traces.
 -keepattributes SourceFile,LineNumberTable
 
+# Allowing Proguard to change modifiers (e.g. private->public).
+-allowaccessmodification
+
+# Enable protobuf-related optimizations.
+-shrinkunusedprotofields
+
 # Keep all CREATOR fields within Parcelable that are kept.
 -keepclassmembers class * implements android.os.Parcelable {
   public static *** CREATOR;
@@ -47,24 +50,6 @@
   static boolean 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
-
-# Horizontal class merging marginally increases dex size (as of Mar 2018).
--optimizations !class/merging/horizontal
-
-# Allowing Proguard to change modifiers. This change shrinks the .dex size by
-# ~1%, and reduces the method count by ~4%.
--allowaccessmodification
-
 # Workaround for crbug/1002847. Methods of BaseGmsClient are incorrectly
 # removed even though they are required for the derived class GmsClient
 # to correctly implement Api$Client.

chrome/android/java/monochrome_public_bundle.proguard_flags.expected

@@ -82,12 +82,15 @@
 
 # Contains flags that we'd like all Chromium .apks to use.
 
-# Not needed for Android and saves a bit of processing time.
--dontpreverify
-
 # Keep line number information, useful for stack traces.
 -keepattributes SourceFile,LineNumberTable
 
+# Allowing Proguard to change modifiers (e.g. private->public).
+-allowaccessmodification
+
+# Enable protobuf-related optimizations.
+-shrinkunusedprotofields
+
 # Keep all CREATOR fields within Parcelable that are kept.
 -keepclassmembers class * implements android.os.Parcelable {
   public static *** CREATOR;
@@ -125,24 +128,6 @@
   static boolean 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
-
-# Horizontal class merging marginally increases dex size (as of Mar 2018).
--optimizations !class/merging/horizontal
-
-# Allowing Proguard to change modifiers. This change shrinks the .dex size by
-# ~1%, and reduces the method count by ~4%.
--allowaccessmodification
-
 # Workaround for crbug/1002847. Methods of BaseGmsClient are incorrectly
 # removed even though they are required for the derived class GmsClient
 # to correctly implement Api$Client.