project.py: always download sources

Instead of downloading the sources optionally, always download them.
This will help to catch problems introduced in the build that prevent
the sources from downloading (see [1] for example).

Keep the --src option but mark it as deprecated.

Add a new --no-src option to explicitly prevent download of sources.

[1] https://gerrit-review.googlesource.com/#/c/74859/

Change-Id: I9b6a9e210f83fe6a5663011dc5c0daeaa2f7fe46
diff --git a/Documentation/dev-buck.txt b/Documentation/dev-buck.txt
index 6f94fca..d0b2ddc 100644
--- a/Documentation/dev-buck.txt
+++ b/Documentation/dev-buck.txt
@@ -81,13 +81,15 @@
 
 === Attaching Sources
 
-To save time and bandwidth source JARs are only downloaded by the buck
-build where necessary to compile Java source into JavaScript using the
-GWT compiler.  Additional sources may be obtained, allowing Eclipse to
-show documentation or dive into the implementation of a library JAR:
+Source JARs are downloaded by default. This allows Eclipse to show
+documentation or dive into the implementation of a library JAR.
+
+To save time and bandwidth, download of source JARs can be restricted
+to only those that are necessary to compile Java source into JavaScript
+using the GWT compiler:
 
 ----
-  tools/eclipse/project.py --src
+  tools/eclipse/project.py --no-src
 ----
 
 
diff --git a/tools/eclipse/project.py b/tools/eclipse/project.py
index a156cd0..26b35cf 100755
--- a/tools/eclipse/project.py
+++ b/tools/eclipse/project.py
@@ -36,7 +36,10 @@
   ROOT = path.dirname(ROOT)
 
 opts = OptionParser()
-opts.add_option('--src', action='store_true')
+opts.add_option('--src', action='store_true',
+                help='(deprecated) attach sources')
+opts.add_option('--no-src', dest='no_src', action='store_true',
+                help='do not attach sources')
 opts.add_option('--plugins', help='create eclipse projects for plugins',
                 action='store_true')
 args, _ = opts.parse_args()
@@ -215,7 +218,7 @@
     doc.writexml(fd, addindent='\t', newl='\n', encoding='UTF-8')
 
 try:
-  if args.src:
+  if not args.no_src:
     try:
       check_call([path.join(ROOT, 'tools', 'download_all.py'), '--src'])
     except CalledProcessError as err: