[Extensions] Reduce string copy in renderer/ UserScript.

extensions/renderer/user_script_injector.cc

Index: extensions/renderer/user_script_injector.cc
diff --git a/extensions/renderer/user_script_injector.cc b/extensions/renderer/user_script_injector.cc
index 21a59eac30fa4bd3e03c928090db5f13e6189ed9..c9bd11e9935612bda3037b859bbe788c9c7e94b6 100644
--- a/extensions/renderer/user_script_injector.cc
+++ b/extensions/renderer/user_script_injector.cc
@@ -207,16 +207,25 @@ std::vector<blink::WebScriptSource> UserScriptInjector::GetJsSources(
   for (UserScript::FileList::const_iterator iter = js_scripts.begin();
        iter != js_scripts.end();
        ++iter) {
-    std::string content = iter->GetContent().as_string();
-
-    // We add this dumb function wrapper for user scripts to emulate what
-    // Greasemonkey does.
+    base::StringPiece script_content = iter->GetContent();
     if (script_->emulate_greasemonkey()) {
-      content.insert(0, kUserScriptHead);
-      content += kUserScriptTail;
+      // We add this dumb function wrapper for user scripts to emulate what
+      // Greasemonkey does: |script_content| becomes:

[Devlin, 2016/08/18 17:08:16]

nit: replace the first ':' (after 'does') with a '.'.

[lazyboy, 2016/08/18 18:53:23]

Done.

+      // concat(kUserScriptHead, script_content, kUserScriptTail)
+      std::string content;
+      content.reserve(strlen(kUserScriptHead) + content.length() +
+                      strlen(kUserScriptTail));
+      content.append(kUserScriptHead);
+      script_content.AppendToString(&content);
+      content.append(kUserScriptTail);
+      sources.push_back(blink::WebScriptSource(
+          blink::WebString::fromUTF8(content), iter->url()));
+    } else {
+      sources.push_back(blink::WebScriptSource(

[Devlin, 2016/08/18 17:08:16]

We should keep some kind of TODO here to optimize this yet more.

[lazyboy, 2016/08/18 18:53:23]

Done.

+          blink::WebString::fromUTF8(script_content.data(),

[Devlin, 2016/08/18 17:08:16]

hmm... I find it slightly more readable when we reuse the construction of the
WebScriptSource and appending to sources, i.e.

blink::WebString source;
if (greasemonkey) {
  std::string content;
  ...
  source = blink::WebString::fromUTF8(content);
} else {
  source = blink::WebString::fromUTF8(script_content.data(),
script_content.lenght());
}
sources.push_back(blink::WebScriptSource(source, iter->url()));

But that's just me, and I don't feel super strongly.

[lazyboy, 2016/08/18 18:53:23]

Done.

+                                     script_content.length()),
+          iter->url()));
     }
-    sources.push_back(blink::WebScriptSource(
-        blink::WebString::fromUTF8(content), iter->url()));
   }
 
   // Emulate Greasemonkey API for scripts that were converted to extension
@@ -227,19 +236,22 @@ std::vector<blink::WebScriptSource> UserScriptInjector::GetJsSources(
   return sources;
 }
 
-std::vector<std::string> UserScriptInjector::GetCssSources(
+std::vector<blink::WebString> UserScriptInjector::GetCssSources(
     UserScript::RunLocation run_location) const {
   DCHECK_EQ(UserScript::DOCUMENT_START, run_location);
 
-  std::vector<std::string> sources;
+  std::vector<blink::WebString> sources;
   if (!script_)
     return sources;
 
   const UserScript::FileList& css_scripts = script_->css_scripts();
+  sources.reserve(css_scripts.size());
   for (UserScript::FileList::const_iterator iter = css_scripts.begin();
        iter != css_scripts.end();
        ++iter) {
-    sources.push_back(iter->GetContent().as_string());
+    base::StringPiece css_content = iter->GetContent();
+    sources.push_back(
+        blink::WebString::fromUTF8(css_content.data(), css_content.length()));
   }
   return sources;
 }