Configure recipe-based 32-bit Windows Release chromium.webkit builders

BUG=460949
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/977593007

Cr-Commit-Position: refs/heads/master@{#319072}

testing/buildbot/chromium.webkit.json

 {
+  "WebKit XP": {
+    "gtest_tests": [
+      "blink_heap_unittests",
+      "blink_platform_unittests",
+      "webkit_unit_tests",
+      "wtf_unittests"
+    ],
+    "scripts": [
+      {
+        "name": "webkit_lint",
+        "script": "webkit_lint.py"
+      },
+      {
+        "name": "webkit_python_tests",
+        "script": "webkit_python_tests.py"
+      }
+    ]
+  },
+  "WebKit Win7": {
+    "gtest_tests": [
+      "blink_heap_unittests",
+      "blink_platform_unittests",
+      "webkit_unit_tests",
+      "wtf_unittests"
+    ],
+    "scripts": [
+      {
+        "name": "webkit_lint",
+        "script": "webkit_lint.py"
+      },
+      {
+        "name": "webkit_python_tests",
+        "script": "webkit_python_tests.py"
+      }
+    ]
+  },
   "WebKit Linux": {
     "gtest_tests": [
       "blink_heap_unittests",