Adds UMA for slow and fast back/forward WKWebController navigations.

ios/web/web_state/ui/crw_web_controller.mm

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/web/web_state/ui/crw_web_controller.h"
 
 #import <objc/runtime.h>
 #include <stddef.h>
 
 #include <cmath>
@@ skipping 148 matching lines @@
 
   // All user gestures are handled by a subview of web view scroll view
   // (UIWebBrowserView for UIWebView and WKContentView for WKWebView).
   for (UIView* subview in web_scroll_view.subviews) {
     for (UIGestureRecognizer* recognizer in subview.gestureRecognizers) {
       CancelTouches(recognizer);
     }
   }
 }
 
+// Key of the UMA Navigation.IOSWKWebViewSlowFastBackForward histogram.
+const char kUMAWKWebViewSlowFastBackForwardNavigationKey[] =
+    "Navigation.IOSWKWebViewSlowFastBackForward";
+
+// Values for the histogram that counts slow/fast back/forward navigations.
+enum BackForwardNavigationType {
+  // Fast back navigation through WKWebView back-forward list.
+  FAST_BACK = 0,

[Eugene But (OOO till 7-30), 2016/01/20 16:45:04]

Back usually means previous (not negative delta), also distinguishing between
back/forward/delta in probably unnecessary. With that I think we need 2 metrics:
FAST and SLOW.

[stkhapugin, 2016/01/21 10:39:36]

Stuart mentioned that he'd like to have a distinction between back/forward,
although it's not necessary. Now that I understand how to implement it, why
don't we keep the two? I think there is little reason to distinguish between "go
back one page" and "go back (>1) pages", too. 
Stuart, what do you think? 

[Eugene But (OOO till 7-30), 2016/01/21 15:03:49]

The problem here is that FAST_BACK is misleading, because it also contains
negative delta.

[stuartmorgan, 2016/01/28 23:25:44]

By "negative delta" do you mean going back N>1 pages? I think that's fine
personally, but having either more (1 vs >1 in each direction) or fewer (just
fast or slow history) buckets is fine with me as well.

+  // Slow back navigation when back-forward list navigation is not possible.
+  SLOW_BACK,
+  // Fast forward navigation through WKWebView back-forward list.
+  FAST_FORWARD,
+  // Slow forward navigation when back-forward list navigation is not possible.
+  SLOW_FORWARD,
+  BACK_FORWARD_NAVIGATION_TYPE_COUNT
+};
+
 }  // namespace
 
 @interface CRWWebController () <CRWNativeContentDelegate,
                                 CRWWebControllerContainerViewDelegate,
                                 CRWWebViewScrollViewProxyObserver> {
   base::WeakNSProtocol<id<CRWWebDelegate>> _delegate;
   base::WeakNSProtocol<id<CRWWebUserInterfaceDelegate>> _UIDelegate;
   base::WeakNSProtocol<id<CRWNativeContentProvider>> _nativeProvider;
   base::WeakNSProtocol<id<CRWSwipeRecognizerProvider>> _swipeRecognizerProvider;
   // The CRWWebViewProxy is the wrapper to give components access to the
@@ skipping 1500 matching lines @@
         self.webStateImpl->GetRequestTracker()->FinishPageLoad(
             _URLOnStartLoading, false);
       }
       [_delegate webLoadCancelled:_URLOnStartLoading];
       break;
     case web::PAGE_LOADED:
       break;
   }
 }
 
+- (BOOL)canPerformFastNavigationForSessionEntry:(CRWSessionEntry*)sessionEntry {
+  // Should be overriden by subclasses if they support fast navigation.
+  return NO;
+}
+
 - (void)abortLoad {
   [self abortWebLoad];
   [self loadCancelled];
 }
 
 - (void)prepareForGoBack {
   // Make sure any transitions that may have occurred have been seen and acted
   // on by the CRWWebController, so the history stack and state of the
   // CRWWebController is 100% up to date before the stack navigation starts.
   if (self.webView) {
@@ skipping 47 matching lines @@
   // fromEntry is retained because it has the potential to be released
   // by goDelta: if it has not been committed.
   base::scoped_nsobject<CRWSessionEntry> fromEntry(
       [[sessionController currentEntry] retain]);
   [sessionController goDelta:delta];
   if (fromEntry) {
     _webStateImpl->SetCacheMode(net::RequestTracker::CACHE_HISTORY);
     [self finishHistoryNavigationFromEntry:fromEntry];
     _webStateImpl->SetCacheMode(net::RequestTracker::CACHE_NORMAL);
   }
+
+  // If using WKWebView, report slow/fast navigation metric.
+  if ([self isKindOfClass:[CRWWKWebViewWebController class]]) {

[Eugene But (OOO till 7-30), 2016/01/20 16:45:04]

I think you should move this code to subclass' goDelta: Hardcoding classname is
not maintainable. Also this way you won't need
canPerformFastNavigationForSessionEntry:

[stkhapugin, 2016/01/21 10:39:36]

Done.

+    BOOL isFast =
+        [self canPerformFastNavigationForSessionEntry:self.currentSessionEntry];
+    BOOL isBack = (delta < 0);
+
+    BackForwardNavigationType navigationType;

[Eugene But (OOO till 7-30), 2016/01/20 16:45:04]

Please always initialize local variables.

[stkhapugin, 2016/01/21 10:39:36]

Done.

+    if (isBack) {
+      navigationType = isFast ? BackForwardNavigationType::FAST_BACK
+                              : BackForwardNavigationType::SLOW_BACK;
+    } else {
+      navigationType = isFast ? BackForwardNavigationType::FAST_FORWARD
+                              : BackForwardNavigationType::SLOW_FORWARD;
+    }
+
+    UMA_HISTOGRAM_ENUMERATION(
+        kUMAWKWebViewSlowFastBackForwardNavigationKey, navigationType,
+        BackForwardNavigationType::BACK_FORWARD_NAVIGATION_TYPE_COUNT);
+  }
 }
 
 - (BOOL)isLoaded {
   return _loadPhase == web::PAGE_LOADED;
 }
 
 - (void)loadCompleteWithSuccess:(BOOL)loadSuccess {
   [self removePlaceholderOverlay];
   // The webView may have been torn down (or replaced by a native view). Be
   // safe and do nothing if that's happened.
@@ skipping 2143 matching lines @@
   if ([MIMEType isEqualToString:@"text/html"] ||
       [MIMEType isEqualToString:@"application/xhtml+xml"] ||
       [MIMEType isEqualToString:@"application/xml"]) {
     return web::WEB_VIEW_DOCUMENT_TYPE_HTML;
   }
 
   return web::WEB_VIEW_DOCUMENT_TYPE_GENERIC;
 }
 
 @end