Generate snapshot for dartj2s; use it in the SDK.

dart/utils/compiler/compiler.gyp

Index: dart/utils/compiler/compiler.gyp
diff --git a/dart/utils/compiler/compiler.gyp b/dart/utils/compiler/compiler.gyp
index d419a5f5d912dbefbe0990e29f0d7aa3108d92d4..9b5ae690bbed2027b49eddbae6d02404f95cf2f0 100644
--- a/dart/utils/compiler/compiler.gyp
+++ b/dart/utils/compiler/compiler.gyp
@@ -45,6 +45,28 @@
             '<(dart_dir)',
           ],
         },
+        {
+          'action_name': 'generate_dart2js_snapshot',
+          'inputs': [
+            '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)gen_snapshot<(EXECUTABLE_SUFFIX)',
+            '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)dart<(EXECUTABLE_SUFFIX)',
+            '../../lib/_internal/libraries.dart',
+            '<!@(["python", "../../tools/list_files.py", "\\.dart$", "../../lib/compiler", "../../runtime/lib"])',
+          ],
+          'outputs': [
+            '<(PRODUCT_DIR)/dart2js.snapshot',
+          ],
+          'action': [
+            '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)gen_snapshot<(EXECUTABLE_SUFFIX)',
+            # Note: we don't store the snapshot in the location where
+            # the dart2js script is looking for it.  The motivation
+            # for that is to support an incremental development model
+            # for dart2js compiler engineers.  However, we install the
+            # snapshot in the proper location when building the SDK.
+            '--script_snapshot=<(PRODUCT_DIR)/dart2js.snapshot',
+            '../../lib/compiler/implementation/dart2js.dart',
+          ],
+        },
       ],
     },
   ],