Replace requirePageReconstruction with setCustomUserAgent

ios/web/web_state/ui/crw_web_controller.mm

Index: ios/web/web_state/ui/crw_web_controller.mm
diff --git a/ios/web/web_state/ui/crw_web_controller.mm b/ios/web/web_state/ui/crw_web_controller.mm
index 4d87b2c3da8df85af85d482cbd6a74a833044682..229a1c77fe2b78196469381a39ca1a4c82b9e860 100644
--- a/ios/web/web_state/ui/crw_web_controller.mm
+++ b/ios/web/web_state/ui/crw_web_controller.mm
@@ -459,8 +459,10 @@ @interface CRWWebController ()<CRWContextMenuDelegate,
 // Returns YES if the user interacted with the page recently.
 @property(nonatomic, readonly) BOOL userClickedRecently;
 
-// Whether or not desktop user agent is used for the currentItem.
-@property(nonatomic, readonly) BOOL usesDesktopUserAgent;
+// User agent type of the transient item if any, the pending item if a
+// navigation is in progress or the last committed item otherwise.
+// Returns MOBILE, the default type, if navigation manager is nullptr or empty.
+@property(nonatomic, readonly) web::UserAgentType userAgentType;
 
 // Facade for Mojo API.
 @property(nonatomic, readonly) web::MojoFacade* mojoFacade;
@@ -477,10 +479,10 @@ @interface CRWWebController ()<CRWContextMenuDelegate,
 // unless the request was a POST.
 @property(nonatomic, readonly) NSDictionary* currentHTTPHeaders;
 
-// Requires page reconstruction if |item| has a non-NONE UserAgentType and it
-// differs from that of |fromItem|.
-- (void)updateDesktopUserAgentForItem:(web::NavigationItem*)item
-                previousUserAgentType:(web::UserAgentType)userAgentType;
+// Updates the user agent used to make HTTP request if |item|'s user agent type
+// is not NONE and has changed.
+- (void)updateUserAgentForItem:(web::NavigationItem*)item

[Eugene But (OOO till 7-30), 2017/04/12 18:22:02]

updateWebViewUserAgentFromItem: ?

[liaoyuke, 2017/04/12 19:17:59]

Thanks! that's even better, and after looking at the caller place, I think it
makes more sense to pass in two items instead of an item and a user agent type.

+         previousUserAgentType:(web::UserAgentType)previousUserAgentType;
 
 // Removes the container view from the hierarchy and resets the ivar.
 - (void)resetContainerView;
@@ -1616,6 +1618,10 @@ - (void)loadCurrentURLInWebView {
 
   [self ensureWebViewCreated];
 
+  NSString* userAgent = base::SysUTF8ToNSString(
+      web::GetWebClient()->GetUserAgent(self.userAgentType));
+  [_webView setCustomUserAgent:userAgent];

[Eugene But (OOO till 7-30), 2017/04/12 18:22:02]

Are there any performance implications in calling this for every load? This call
can potentially send a message to a separate process.

[liaoyuke, 2017/04/12 19:17:59]

That is a very good question. I'm not sure how WKWebView works, is it no-op if
|userAgent| is the same as WKWebView's current user agent?

Calling this for every load is simple and clean, so as long as [_webView
setCustomUserAgent:userAgent]; is not causing any noticeable delay, I think it
worths the overhead, WDYT?

[Eugene But (OOO till 7-30), 2017/04/13 00:34:06]

WKWebView code is open source, so it should not be hard to check.

[liaoyuke, 2017/04/13 23:03:53]

Sorry, forgot to reply. I was only able to find the header file of WKWebView,
but not source file, so I still don't know if there is performance implications.

[Eugene But (OOO till 7-30), 2017/04/14 00:19:53]

WKWebView source code:
https://trac.webkit.org/browser/webkit/trunk/Source/WebKit2/UIProcess/API/Cocoa

More info on WebKit:
https://webkit.org/getting-the-code/

+
   [self loadRequestForCurrentNavigationItem];
 }
 
@@ -2030,8 +2036,8 @@ - (void)goToItemAtIndex:(int)index {
   web::UserAgentType previousUserAgentType =
       previousItem ? previousItem->GetUserAgentType()
                    : web::UserAgentType::NONE;
-  [self updateDesktopUserAgentForItem:toItem
-                previousUserAgentType:previousUserAgentType];
+  [self updateUserAgentForItem:toItem
+         previousUserAgentType:previousUserAgentType];
 
   BOOL sameDocumentNavigation =
       [sessionController isSameDocumentNavigationBetweenItem:previousItem
@@ -2189,9 +2195,11 @@ - (BOOL)shouldClosePageOnNativeApplicationLoad {
   return rendererInitiatedWithoutInteraction || noNavigationItems;
 }
 
-- (BOOL)usesDesktopUserAgent {
-  web::NavigationItem* item = self.currentNavItem;
-  return item && item->GetUserAgentType() == web::UserAgentType::DESKTOP;
+- (web::UserAgentType)userAgentType {
+  if (!self.currentNavItem)

[Eugene But (OOO till 7-30), 2017/04/12 18:22:02]

Old code with ternary could be faster

[liaoyuke, 2017/04/12 19:17:59]

Done.

+    return web::UserAgentType::MOBILE;
+
+  return self.currentNavItem->GetUserAgentType();
 }
 
 - (web::MojoFacade*)mojoFacade {
@@ -2230,15 +2238,19 @@ - (CRWPassKitDownloader*)passKitDownloader {
   return _passKitDownloader.get();
 }
 
-- (void)updateDesktopUserAgentForItem:(web::NavigationItem*)item
-                previousUserAgentType:(web::UserAgentType)userAgentType {
+- (void)updateUserAgentForItem:(web::NavigationItem*)item
+         previousUserAgentType:(web::UserAgentType)previousUserAgentType {
   if (!item)
     return;
-  web::UserAgentType itemUserAgentType = item->GetUserAgentType();
-  if (itemUserAgentType == web::UserAgentType::NONE)
+  web::UserAgentType currentUserAgentType = item->GetUserAgentType();

[Eugene But (OOO till 7-30), 2017/04/12 18:22:02]

This isn't "current", right? Current is one that is used in WKWebView.

[liaoyuke, 2017/04/12 19:17:59]

Done.

+  if (currentUserAgentType == web::UserAgentType::NONE)
     return;
-  if (itemUserAgentType != userAgentType)
-    [self requirePageReconstruction];
+
+  if (currentUserAgentType != previousUserAgentType) {
+    NSString* currentUserAgent = base::SysUTF8ToNSString(

[Eugene But (OOO till 7-30), 2017/04/12 18:22:02]

ditto

[liaoyuke, 2017/04/12 19:17:59]

Done.

+        web::GetWebClient()->GetUserAgent(currentUserAgentType));
+    [_webView setCustomUserAgent:currentUserAgent];
+  }
 }
 
 #pragma mark -
@@ -4040,7 +4052,7 @@ - (WKWebView*)webViewWithConfiguration:(WKWebViewConfiguration*)config {
   // delegate must be specified.
   return web::BuildWKWebView(CGRectZero, config,
                              self.webStateImpl->GetBrowserState(),
-                             self.usesDesktopUserAgent);
+                             self.userAgentType);
 }
 
 - (void)setWebView:(WKWebView*)webView {