mojo: Add DataURLFetcher for processing data: urls.

mojo/fetcher/BUILD.gn

Index: mojo/fetcher/BUILD.gn
diff --git a/mojo/fetcher/BUILD.gn b/mojo/fetcher/BUILD.gn
index f362129f86a9ecc37834ae82feecae650dc11604..4c3311a22f9667e35ec1379351d0d3d254635d31 100644
--- a/mojo/fetcher/BUILD.gn
+++ b/mojo/fetcher/BUILD.gn
@@ -10,6 +10,8 @@ source_set("fetcher") {
     "about_fetcher.h",
     "base_application_fetcher.cc",
     "base_application_fetcher.h",
+    "data_fetcher.cc",
+    "data_fetcher.h",
     "local_fetcher.cc",
     "local_fetcher.h",
     "network_fetcher.cc",
@@ -40,5 +42,6 @@ source_set("fetcher") {
     "//mojo/environment:chromium",
     "//mojo/shell",
     "//mojo/util:filename_util",
+    "//net",
   ]
 }