Add support for an optional "requirements" section in extension/app manifests.

chrome/test/data/extensions/manifest_tests/init_valid_app_requirements.json

Index: chrome/test/data/extensions/manifest_tests/init_valid_app_requirements.json
diff --git a/chrome/test/data/extensions/manifest_tests/init_valid_app_requirements.json b/chrome/test/data/extensions/manifest_tests/init_valid_app_requirements.json
new file mode 100644
index 0000000000000000000000000000000000000000..c6b82aa1748e3c6162bec3c2ffefce8b6d46a319
--- /dev/null
+++ b/chrome/test/data/extensions/manifest_tests/init_valid_app_requirements.json
@@ -0,0 +1,17 @@
+{
+  "name": "Requirements Hosted App",
+  "version": "0",
+  "app": {
+    "launch": {
+      "web_url": "http://example.com"
+    },
+    "urls": [
+      "http://*.example.com"
+    ]
+  },
+  "requirements": {
+    "webgl": {
+      "extensions": ["l33t OpenGL extension"]
+    }
+  }
+}