percent-encode U+0020 SPACE when using a protocol handler

Currently, URLs calculated by protocol handlers escape spaces as "+".
This CL changes this to use "%20" instead, aligning with Firefox and
the specification.

For details, read the following links:
https://chromestatus.com/feature/5678518908223488
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/osabCTBhDSs
https://bugs.chromium.org/p/chromium/issues/detail?id=795919
https://html.spec.whatwg.org/multipage/system-state.html#custom-handlers
https://github.com/whatwg/html/issues/3377

Bug: 1110842
Change-Id: I31e2250c56d3c4654d5a8655ead953af33b5fb5c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2324126Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Frédéric Wang <fwang@igalia.com>
Cr-Commit-Position: refs/heads/master@{#799541}

chrome/browser/custom_handlers/protocol_handler_registry_unittest.cc

@@ -977,9 +977,8 @@ TEST_F(ProtocolHandlerRegistryTest, TestURIPercentEncoding) {
 
   // Space character.
   translated_url = ph.TranslateUrl(GURL("web+custom://custom handler"));
-  // TODO(mgiuca): Check whether this(' ') should be encoded as '%20'.
   ASSERT_EQ(translated_url,
-            GURL("https://test.com/url=web%2Bcustom%3A%2F%2Fcustom+handler"));
+            GURL("https://test.com/url=web%2Bcustom%3A%2F%2Fcustom%20handler"));
 
   // Query parameters.
   translated_url = ph.TranslateUrl(GURL("web+custom://custom?foo=bar&bar=baz"));

chrome/common/custom_handlers/protocol_handler.cc

@@ -98,7 +98,7 @@ GURL ProtocolHandler::TranslateUrl(const GURL& url) const {
   std::string translatedUrlSpec(url_.spec());
   base::ReplaceFirstSubstringAfterOffset(
       &translatedUrlSpec, 0, "%s",
-      net::EscapeQueryParamValue(url.spec(), true));
+      net::EscapeQueryParamValue(url.spec(), false));
   return GURL(translatedUrlSpec);
 }