Make javac invocations incremental when possible

build/config/android/internal_rules.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.
 
 import("//build/config/android/config.gni")
 import("//build/config/zip.gni")
 import("//third_party/ijar/ijar.gni")
 
 assert(is_android)
 
@@ skipping 1103 matching lines @@
     _rebased_depfile = rebase_path(depfile, root_build_dir)
     args = [
       "--depfile=$_rebased_depfile",
       "--use-ijars",
       "--classpath=@FileArg($_rebased_build_config:javac:classpath)",
       "--jar-path=$_rebased_jar_path",
       "--java-srcjars=$_rebased_java_srcjars",
       "--java-srcjars=@FileArg($_rebased_build_config:javac:srcjars)",
       "--jar-excluded-classes=$_jar_excluded_patterns",
     ]
+    if (incremental_javac) {
+      args += [ "--incremental" ]
+    }
     if (_supports_android) {
       deps += [ "//build/android:android_ijar" ]
       _android_sdk_ijar = "$root_out_dir/lib.java/android.interface.jar"
       inputs += [ _android_sdk_ijar ]
       _rebased_android_sdk_ijar = rebase_path(_android_sdk_ijar, root_build_dir)
       args += [ "--bootclasspath=$_rebased_android_sdk_ijar" ]
     }
     foreach(e, _manifest_entries) {
       args += [ "--manifest-entry=" + e ]
     }
@@ skipping 514 matching lines @@
     ]
     args = [
       "--depfile",
       rebase_path(depfile, root_build_dir),
       "--script-output-path",
       rebase_path(generated_script, root_build_dir),
     ]
     args += test_runner_args
   }
 }