Advertise DocumentPolicy & Network Err when receive incompatible policy

- Advertise required document policy on out-going requests.
- Parse and initialize document policy in security context.
- Replace with page with empty document when incoming document policy
is incompatible with required policy.
- A boolean flag body_loader_finished is added to SimRequestBase::Finish
because when testing page blocked by document policy situation in
document_loader_test.cc, body_loader.Finish will be called twice, once
in WebNavigationParams::FillStaticResponse, once in test framework, which
will crash the test because of a DCHECK.

Bug: 993790
Change-Id: I823675408a0d52e8048172ae23d409a5f14e8eb5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1947187
Commit-Queue: Charlie Hu <chenleihu@google.com>
Reviewed-by: Camille Lamy <clamy@chromium.org>
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#730275}
diff --git a/document-policy/required-policy/document-policy.html b/document-policy/required-policy/document-policy.html
index d6bf3e9..1935be3 100644
--- a/document-policy/required-policy/document-policy.html
+++ b/document-policy/required-policy/document-policy.html
@@ -45,7 +45,7 @@
   iframe.src = "/document-policy/echo-policy.py?id=3";
   iframe.policy = "unoptimized-lossless-images;bpp=4";
   callbacks["3"] = t.step_func_done(result => {
-    assert_equals(result, "unoptimized-lossless-images;bpp=4");
+    assert_equals(result, "unoptimized-lossless-images;bpp=4.0");
   });
   document.body.appendChild(iframe);
 }, "Child frame can have a required policy which is less strict than the parent document's policy.");
diff --git a/document-policy/required-policy/required-document-policy.html.headers b/document-policy/required-policy/required-document-policy.html.headers
index 066c0f8..1b671da 100644
--- a/document-policy/required-policy/required-document-policy.html.headers
+++ b/document-policy/required-policy/required-document-policy.html.headers
@@ -1 +1 @@
-Required-Document-Policy: unoptimized-lossless-images;bpp=1.1
+Require-Document-Policy: unoptimized-lossless-images;bpp=1.1