Document --analyze-all option.

dart/sdk/lib/_internal/compiler/implementation/dart2js.dart

Index: dart/sdk/lib/_internal/compiler/implementation/dart2js.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/dart2js.dart b/dart/sdk/lib/_internal/compiler/implementation/dart2js.dart
index c653e2f68a354518adfd740e5cdf2106dc4eeb27..3af4ac14ba0c51cd090429ae58a6054726a7151c 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/dart2js.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/dart2js.dart
@@ -375,6 +375,12 @@ Supported options:
   -p<path>, --package-root=<path>
     Where to find packages, that is, "package:..." imports.
 
+  --analyze-all
+    Normally, the compiler only examines code that is reachable from
+    [main].  With this option, it will examine everything.  This is

[asandholm, 2012/11/14 12:46:25]

LGTM with comments. 
I'd probably use "analyze" rather than "examine". Start with what the option
does (not what the default behavior is). The extra info on where this is useful
and the added cost on perf is nice-to-have but not need-to-have IMO.

+    useful for finding errors in libraries, but using this option can
+    result in bigger and slower output.
+
   --minify
     Generate minified output.