Relanding "Add apk for running content_browsertests"

build/java_apk.gypi

Index: build/java_apk.gypi
diff --git a/build/java_apk.gypi b/build/java_apk.gypi
index a8876639bf9152a86f85b75837c5af91143c7e79..fb79797eea700a6f2a7c3b1e776bf4e657fe2f12 100644
--- a/build/java_apk.gypi
+++ b/build/java_apk.gypi
@@ -18,12 +18,10 @@
 #   'includes': ['path/to/this/gypi/file'],
 # }
 #
-# Note that this assumes that there's an ant buildfile <package_name>_apk.xml in
-# java_in_dir. So, if you have package_name="content_shell" and
+# If you have package_name="content_shell" and
 # java_in_dir="content/shell/android/java" you should have a directory structure
 # like:
 #
-# content/shell/android/java/content_shell_apk.xml
 # content/shell/android/java/src/org/chromium/base/Foo.java
 # content/shell/android/java/src/org/chromium/base/Bar.java
 #
@@ -41,8 +39,8 @@
 #    each directory in additional_res_dirs.
 #  additional_src_dirs - Additional directories with .java files to be compiled
 #    and included in the output of this target.
-#  asset_location - The directory where assets are located (default:
-#    <PRODUCT_DIR>/<package_name>/assets).
+#  asset_location - The absolute path to the directory where assets are located
+#    (default: <(ant_build_out)/<(package_name)/assets).
 #  generated_src_dirs - Same as additional_src_dirs except used for .java files
 #    that are generated at build time. This should be set automatically by a
 #    target's dependencies. The .java files in these directories are not