android: Make javac rules depend on java files too.

build/java_apk.gypi

Index: build/java_apk.gypi
diff --git a/build/java_apk.gypi b/build/java_apk.gypi
index 6e28103da6b30861411d21ea78131d3be9fe83e4..d8d8e9d3cee23e30d0bffcd6ba5e11942c243551 100644
--- a/build/java_apk.gypi
+++ b/build/java_apk.gypi
@@ -525,12 +525,14 @@
         # 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)',