Add incremental_apk_by_default GN arg.

build/config/android/config.gni

Index: build/config/android/config.gni
diff --git a/build/config/android/config.gni b/build/config/android/config.gni
index d5948f2fbf373c0b89c3074d912d5b821ffaa450..8bddc27335582bfb542a4f8ec6901d9df012125e 100644
--- a/build/config/android/config.gni
+++ b/build/config/android/config.gni
@@ -146,6 +146,11 @@ if (is_android) {
     # Enables java8 language features (via retrolambda).
     # work-in-progress (http://crbug.com/642600)
     use_java8 = false
+
+    # Build incremental targets whenever possible.
+    # Ex. with this arg set to true, the chrome_public_apk target result in
+    # chrome_public_apk_incremental being built.
+    incremental_apk_by_default = false
   }
 
   # We need a second declare_args block to make sure we are using the overridden