Fix for getContextAttributes which wraps bare dictionary into a Dart type.

tools/dom/docs/docs.json

Index: tools/dom/docs/docs.json
diff --git a/tools/dom/docs/docs.json b/tools/dom/docs/docs.json
index 7494d1f5f5cf87d6d039a858c941be18c12eb51f..a787d3cfe06cddf98c3c35e5ee82aa33ea4642ac 100644
--- a/tools/dom/docs/docs.json
+++ b/tools/dom/docs/docs.json
@@ -530,6 +530,32 @@
     }
   },
   "dart.dom.web_gl": {
+    "WebGLContextAttributes": {
+      "comment": [
+        "/**",
+        " * The properties of a WebGL rendering context.",
+        " *",
+        " * If [alpha] is `true`, then the context has an alpha channel.",
+        " *",
+        " * If [antialias] is `true`, then antialiasing is performed by the browser, but",
+        " * only if the browser's implementation of WebGL supports antialiasing.",
+        " *",
+        " * If [depth] is `true`, then the context has a depth buffer of at least 16",
+        " * bits.",
+        " *",
+        " * If [premultipliedAlpha] is `true`, then the context's colors are assumed to",
+        " * be premultiplied. This means that color values are assumed to have  been",
+        " * multiplied by their alpha values. If [alpha] is `false`, then this flag is",
+        " * ignored.",
+        " *",
+        " * If [preserveDrawingBuffer] is `false`, then all contents of the context are",
+        " * cleared. If `true`, then all values will remain until changed or cleared.",
+        " *",
+        " * If [stencil] is `true`, then the context has a stencil buffer of at least 8",
+        " * bits.",
+        " */"
+      ]
+    },
     "WebGLRenderingContext": {
       "members": {
         "bufferData": [