[filesapp] Add DevToolsListener SpanToStringPiece helper

Add SpanToStringPiece helper and use it handle response messages from
the devtools agent. This avoids the implicit memcpy under-the-hood of
the span to temporary std::string (message) conversion.

Minor: remove unused includes, and add base::span, base::string_piece
includes. No change in behavior.

Tbr: benreich
Bug: 1113941
Change-Id: I9a9295230b0a807d3405d70af92cf32ac88cbdaa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2470280
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816908}

chrome/browser/chromeos/file_manager/devtools_listener.cc

@@ -10,6 +10,7 @@
 #include <string>
 #include <vector>
 
+#include "base/containers/span.h"
 #include "base/files/file_util.h"
 #include "base/hash/md5.h"
 #include "base/json/json_reader.h"
@@ -17,16 +18,20 @@
 #include "base/logging.h"
 #include "base/run_loop.h"
 #include "base/strings/strcat.h"
+#include "base/strings/string_piece.h"
 #include "base/strings/stringprintf.h"
-#include "base/threading/thread_restrictions.h"
 #include "url/url_util.h"
 
 namespace file_manager {
 
 namespace {
 
-base::span<const uint8_t> StringToSpan(const std::string& str) {
-  return base::as_bytes(base::make_span(str));
+base::span<const uint8_t> StringToSpan(const std::string& s) {
+  return base::as_bytes(base::make_span(s));
+}
+
+base::StringPiece SpanToStringPiece(const base::span<const uint8_t>& s) {
+  return {reinterpret_cast<const char*>(s.data()), s.size()};
 }
 
 std::string EncodeURIComponent(const std::string& component) {
@@ -236,15 +241,12 @@ void DevToolsListener::AwaitMessageResponse(int id) {
 
 void DevToolsListener::DispatchProtocolMessage(
     content::DevToolsAgentHost* host,
-    base::span<const uint8_t> span_message) {
+    base::span<const uint8_t> message) {
   if (!navigated_)
     return;
 
-  std::string message(reinterpret_cast<const char*>(span_message.data()),
-                      span_message.size());
-
-  std::unique_ptr<base::DictionaryValue> response =
-      base::DictionaryValue::From(base::JSONReader::ReadDeprecated(message));
+  std::unique_ptr<base::DictionaryValue> response = base::DictionaryValue::From(
+      base::JSONReader::ReadDeprecated(SpanToStringPiece(message)));
   CHECK(response);
 
   std::string* method = response->FindStringPath("method");

chrome/browser/chromeos/file_manager/devtools_listener.h

@@ -66,7 +66,7 @@ class DevToolsListener : public content::DevToolsAgentHostClient {
 
   // Receives CDP messages sent by host.
   void DispatchProtocolMessage(content::DevToolsAgentHost* host,
-                               base::span<const uint8_t> span_message) override;
+                               base::span<const uint8_t> message) override;
 
   // Returns true if URL should be attached to.
   bool MayAttachToURL(const GURL& url, bool is_webui) override;