Initialize ios/web_view translate with a system-wide URLRequestContext.

ios/web_view/internal/cwv_web_view_configuration.mm

Index: ios/web_view/internal/cwv_web_view_configuration.mm
diff --git a/ios/web_view/internal/cwv_web_view_configuration.mm b/ios/web_view/internal/cwv_web_view_configuration.mm
index bd677f49a2b86c7fd42172b5fcd52758f9a42243..49ab5cf643b4c4d20bf3f1740f30c31b606c14c8 100644
--- a/ios/web_view/internal/cwv_web_view_configuration.mm
+++ b/ios/web_view/internal/cwv_web_view_configuration.mm
@@ -9,11 +9,11 @@
 #include "base/threading/thread_restrictions.h"
 #include "components/translate/core/browser/translate_download_manager.h"
 #include "ios/web/public/app/web_main.h"
+#include "ios/web_view/internal/app/application_context.h"
 #import "ios/web_view/internal/cwv_user_content_controller_internal.h"
 #import "ios/web_view/internal/web_view_browser_state.h"
 #import "ios/web_view/internal/web_view_web_client.h"
 #import "ios/web_view/internal/web_view_web_main_delegate.h"
-#include "ui/base/l10n/l10n_util_mac.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
@@ -60,6 +60,15 @@
     webMainDelegate = base::MakeUnique<ios_web_view::WebViewWebMainDelegate>();
     web::WebMainParams params(webMainDelegate.get());
     webMain = base::MakeUnique<web::WebMain>(params);
+
+    // Initialize translate.

[Eugene But (OOO till 7-30), 2017/05/18 23:54:55]

Is this something that can be deferred? Can this affect startup performance?

[michaeldo, 2017/05/19 22:02:36]

This could affect startup performance depending on how the embedder is using the
Framework. (It happens before ios_web_view_shell is done starting up because in
viewDidLoad, the VC creates the web_view.) However, I don't know if we can delay
it's creation. Maybe we could provide API to disable translate altogether which
would likely allow us to not create this at all. I think for now this needs to
happen early until we can do a more in depth investigation of how and where it
could be moved to.

(ios/chrome actually initializes this in
IOSChromeMainParts::PreMainMessageLoopRun and I think in a followup it would be
good to move it there for ios/web_view as well. Note this is crbug.com/723869.
However this will still match the order and timing of how things are run now
very closely.)

[Eugene But (OOO till 7-30), 2017/05/19 23:32:05]

Can we measure how much time does it take to execute the code? Translation does
not work until the keys are set. So maybe this can be done after setting API
keys?

[michaeldo, 2017/05/23 22:38:36]

On my iPhone 7 this code takes about half a millisecond to execute the first
time and only around 0.06 milliseconds on subsequent runs. I ran multiple times
and measured with base::TimeTicks. I don't want to over-optimize this if it
isn't necessary. However, I agree we should delay this if possible, especially
if translate will never be used by the client. Do you think this can wait?

+    translate::TranslateDownloadManager* downloadManager =
+        translate::TranslateDownloadManager::GetInstance();
+    downloadManager->set_request_context(
+        GetApplicationContext()->GetSystemURLRequestContext());
+    downloadManager->set_application_locale(
+        GetApplicationContext()->GetApplicationLocale());
+    downloadManager->language_list()->SetResourceRequestsAllowed(true);
   });
 }
 
@@ -69,15 +78,6 @@
   if (self) {
     _browserState = std::move(browserState);
 
-    // Initialize translate.
-    translate::TranslateDownloadManager* downloadManager =
-        translate::TranslateDownloadManager::GetInstance();
-    // TODO(crbug.com/710948): Use global request context here.
-    downloadManager->set_request_context(_browserState->GetRequestContext());
-    // TODO(crbug.com/679895): Bring up application locale correctly.
-    downloadManager->set_application_locale(l10n_util::GetLocaleOverride());
-    downloadManager->language_list()->SetResourceRequestsAllowed(true);
-
     _userContentController =
         [[CWVUserContentController alloc] initWithConfiguration:self];
   }