Record UseCounter for distrusted Symantec resources

This will allow us to see how many page loads are affected by the Symantec
distrust
(https://security.googleblog.com/2018/03/distrust-of-symantec-pki-immediate.html).

Note that this doesn't cover iframe main resources that fail to load because
they are distrusted.

Bug: 820582
Change-Id: I4a382dc155f0500222d91c7cdd1eb1a15eea32a6
Reviewed-on: https://chromium-review.googlesource.com/957548
Commit-Queue: Emily Stark <estark@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542365}

third_party/WebKit/Source/core/loader/FrameFetchContext.cpp

@@ -661,6 +661,8 @@ void FrameFetchContext::DispatchDidFail(const KURL& url,
   }
 
   if (NetworkUtils::IsLegacySymantecCertError(error.ErrorCode())) {
+    UseCounter::Count(GetFrame()->GetDocument(),
+                      WebFeature::kDistrustedLegacySymantecSubresource);
     GetLocalFrameClient()->ReportLegacySymantecCert(url, true /* did_fail */);
   }
 

third_party/WebKit/public/platform/web_feature.mojom

@@ -1878,6 +1878,7 @@ enum WebFeature {
   kV8PaintWorkletGlobalScope_DevicePixelRatio_AttributeGetter = 2386,
   kCSSSelectorPseudoFocus = 2387,
   kCSSSelectorPseudoFocusVisible = 2388,
+  kDistrustedLegacySymantecSubresource = 2389,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

tools/metrics/histograms/enums.xml

@@ -17958,6 +17958,7 @@ Called by update_net_error_codes.py.-->
       label="V8PaintWorkletGlobalScope_DevicePixelRatio_AttributeGetter"/>
   <int value="2387" label="CSSSelectorPseudoFocus"/>
   <int value="2388" label="CSSSelectorPseudoFocusVisible"/>
+  <int value="2389" label="DistrustedLegacySymantecSubresource"/>
 </enum>
 
 <enum name="FeedbackSource">