Add retrolambda.py and integrate it to build process.

build/config/android/config.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This file contains common system config stuff for the Android build.
 
 if (is_android) {
   assert(rebase_path("//", root_build_dir) == "../../",
          "Android output directory must be nested 2 levels within src/ (" +
              "e.g.: out-gn/Debug). http://crbug.com/412935")
@@ skipping 118 matching lines @@
 
     # EMMA filter string consisting of a list of inclusion/exclusion patterns
     # separated with whitespace and/or comma. Only has effect if
     # emma_coverage==true
     emma_filter = ""
 
     # Disables process isolation when building _incremental targets.
     # Required for Android M+ due to SELinux policies (stronger sandboxing).
     disable_incremental_isolated_processes = false
 
-    # Speed up incremental compiles by compiling only changed files.
+    # Speeds up incremental compiles by compiling only changed files.
     enable_incremental_javac = false
 
     # Adds intrumentation to each function. Writes a file with the order that
     # functions are called at startup.
     use_order_profiling = false
 
     # Builds secondary abi for APKs, supports build 32-bit arch as secondary
     # abi in 64-bit Monochrome and WebView.
     build_apk_secondary_abi = true
+
+    # Enables java8 language features (via retrolambda).

[agrieve, 2016/11/30 21:54:42]

nit: please add "work-in-progress (http://crbug.com/642600)"

[F, 2016/12/01 15:09:51]

Done.

+    use_java8 = false
   }
 
   # We need a second declare_args block to make sure we are using the overridden
   # value of the arguments set above.
   declare_args() {
     # Speed up dexing using dx --incremental.
     enable_incremental_dx = is_java_debug
   }
 
   # Neither of these should ever be used for release builds since they are
@@ skipping 181 matching lines @@
           "//build/toolchain/android:android_${android_secondary_abi_cpu}"
     }
   }
 }
 
 declare_args() {
   # Enables used resource whitelist generation. Set for official builds only
   # as a large amount of build output is generated.
   enable_resource_whitelist_generation = is_android && is_official_build
 }