android: Make javac rules depend on java files too.

build/java_apk.gypi

 # Copyright (c) 2012 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 is meant to be included into a target to provide a rule
 # to build Android APKs in a consistent manner.
 #
 # To use this, create a gyp target with the following form:
 # {
 #   'target_name': 'my_package_apk',
@@ skipping 507 matching lines @@
         # If there is a separate find for additional_src_dirs, it will find the
         # wrong .java files when additional_src_dirs is empty.
         # TODO(thakis): Gyp caches >! evaluation by command. Both java.gypi and
         # java_apk.gypi evaluate the same command, and at the moment two targets
         # set java_in_dir to "java". Add a dummy comment here to make sure
         # that the two targets (one uses java.gypi, the other java_apk.gypi)
         # get distinct source lists. Medium-term, make targets list all their
         # Java files instead of using find. (As is, this will be broken if two
         # targets use the same java_in_dir and both use java_apk.gypi or
         # both use java.gypi.)
-        'java_source_list': '>|(javasources.<(_target_name).gypcmd >!@(find >(java_in_dir)/src >(additional_src_dirs) -name "*.java"  # apk))',
+        'java_sources': ['>!@(find >(java_in_dir)/src >(additional_src_dirs) -name "*.java"  # apk)'],
+        'java_source_list': '>|(javasources.<(_target_name).gypcmd >@(java_sources))',
 
       },
       'inputs': [
         '<(DEPTH)/build/android/gyp/util/build_utils.py',
         '<(DEPTH)/build/android/gyp/javac.py',
+        '>@(java_sources)',
         '>(java_source_list)',
         '>@(input_jars_paths)',
         '<(codegen_stamp)',
       ],
       'conditions': [
         ['native_lib_target != ""', {
           'inputs': [ '<(native_libraries_java_stamp)' ],
         }],
       ],
       'outputs': [
@@ skipping 216 matching lines @@
         '<(DEPTH)/build/android/ant/apk-package.xml',
 
         # Add list of inputs to the command line, so if inputs change
         # (e.g. if a Java file is removed), the command will be re-run.
         # TODO(newt): remove this once crbug.com/177552 is fixed in ninja.
         '-DTHIS_IS_IGNORED=>!(echo \'>(_inputs)\' | md5sum)',
       ]
     },
   ],
 }