make ParseURL getQuery helper static

Summary:
1. The only callsite of this seemed to migrate to `HTTPMessage::getQueryParam`
2. I was looking to reuse this method, but it requires me to have a `ParsedURL` which is only buildable via URL parsing. This method doesn't really use internal state, so maybe it can just be a static helper.

See next diff for usage.

Reviewed By: lnicco

Differential Revision: D68833844

fbshipit-source-id: 990ff1b621e9b505a387b02c2d1a5669aa09625b

proxygen/lib/utils/ParseURL.cpp

@@ -255,10 +255,9 @@ void ParseURL::stripBrackets() noexcept {
 }
 
 folly::Optional<folly::StringPiece> ParseURL::getQueryParam(
-    folly::StringPiece name) const noexcept {
-  auto params = query_;
-  while (!params.empty()) {
-    auto param = params.split_step('&');
+    folly::StringPiece query, const folly::StringPiece name) noexcept {
+  while (!query.empty()) {
+    auto param = query.split_step('&');
     if (!param.removePrefix(name)) {
       continue;
     }

proxygen/lib/utils/ParseURL.h

@@ -158,8 +158,8 @@ class ParseURL {
 
   FB_EXPORT void stripBrackets() noexcept;
 
-  FOLLY_NODISCARD folly::Optional<folly::StringPiece> getQueryParam(
-      folly::StringPiece name) const noexcept;
+  FOLLY_NODISCARD static folly::Optional<folly::StringPiece> getQueryParam(
+      folly::StringPiece query, const folly::StringPiece name) noexcept;
 
  private:
   void moveHostAndAuthority(ParseURL&& goner) {

proxygen/lib/utils/test/ParseURLTest.cpp

@@ -268,11 +268,12 @@ TEST(ParseURL, PortOverflow) {
 
 TEST(ParseURL, GetQueryParam) {
   auto u = ParseURL::parseURL("localhost/?foo=1&bar=2&baz&bazz=3&bak=");
+  auto q = u->query();
   ASSERT_TRUE(u.hasValue());
-  EXPECT_EQ(u->getQueryParam("foo"), "1");
-  EXPECT_EQ(u->getQueryParam("bar"), "2");
-  EXPECT_EQ(u->getQueryParam("baz"), "");
-  EXPECT_EQ(u->getQueryParam("bazz"), "3");
-  EXPECT_EQ(u->getQueryParam("bak"), "");
-  EXPECT_FALSE(u->getQueryParam("fooo").has_value());
+  EXPECT_EQ(ParseURL::getQueryParam(q, "foo"), "1");
+  EXPECT_EQ(ParseURL::getQueryParam(q, "bar"), "2");
+  EXPECT_EQ(ParseURL::getQueryParam(q, "baz"), "");
+  EXPECT_EQ(ParseURL::getQueryParam(q, "bazz"), "3");
+  EXPECT_EQ(ParseURL::getQueryParam(q, "bak"), "");
+  EXPECT_FALSE(ParseURL::getQueryParam(q, "fooo").has_value());
 }