Don't pretty print TransportSecurityState file.

Users don't generally view this file in a text editor, so we should
not pretty print this file, to both speed up loading and reduce our disk
footprint.

We'll soon be keying Expect-CT data by NetworkIsolationKey, which will
also bloat up this file a bit, so let's decrease its size before that
happens.

Bug: 699461, 969893
Change-Id: I2d6815997dd41e2fcfa98f144c783bdd0f5ef583
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2220907Reviewed-by: Nick Harper <nharper@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773275}

net/http/transport_security_persister.cc

@@ -391,8 +391,7 @@ bool TransportSecurityPersister::SerializeData(std::string* output) {
   toplevel.SetKey(kExpectCTKey,
                   SerializeExpectCTData(transport_security_state_));
 
-  base::JSONWriter::WriteWithOptions(
-      toplevel, base::JSONWriter::OPTIONS_PRETTY_PRINT, output);
+  base::JSONWriter::Write(toplevel, output);
   return true;
 }