Add UseCounters for referrerpolicy attributes

BUG=

Review-Url: https://codereview.chromium.org/2628613002
Cr-Commit-Position: refs/heads/master@{#443145}

third_party/WebKit/Source/core/frame/UseCounter.h

@@ -1421,6 +1421,10 @@ class CORE_EXPORT UseCounter {
     TopNavInSandboxWithPerm = 1751,
     TopNavInSandboxWithPermButNoGesture = 1752,
     ReferrerPolicyHeader = 1753,
+    HTMLAnchorElementReferrerPolicyAttribute = 1754,
+    HTMLIFrameElementReferrerPolicyAttribute = 1755,
+    HTMLImageElementReferrerPolicyAttribute = 1756,
+    HTMLLinkElementReferrerPolicyAttribute = 1757,
 
     // Add new features immediately above this line. Don't change assigned
     // numbers of any item, and don't reuse removed slots.

third_party/WebKit/Source/core/html/HTMLAnchorElement.cpp

@@ -415,6 +415,8 @@ void HTMLAnchorElement::handleClick(Event* event) {
       SecurityPolicy::referrerPolicyFromStringWithLegacyKeywords(
           fastGetAttribute(referrerpolicyAttr), &policy) &&
       !hasRel(RelationNoReferrer)) {
+    UseCounter::count(document(),
+                      UseCounter::HTMLAnchorElementReferrerPolicyAttribute);
     request.setHTTPReferrer(SecurityPolicy::generateReferrer(
         policy, completedURL, document().outgoingReferrer()));
   }

third_party/WebKit/Source/core/html/HTMLIFrameElement.cpp

@@ -113,9 +113,12 @@ void HTMLIFrameElement::parseAttribute(
     UseCounter::count(document(), UseCounter::SandboxViaIFrame);
   } else if (name == referrerpolicyAttr) {
     m_referrerPolicy = ReferrerPolicyDefault;
-    if (!value.isNull())
+    if (!value.isNull()) {
       SecurityPolicy::referrerPolicyFromStringWithLegacyKeywords(
           value, &m_referrerPolicy);
+      UseCounter::count(document(),
+                        UseCounter::HTMLIFrameElementReferrerPolicyAttribute);
+    }
   } else if (name == allowfullscreenAttr) {
     bool oldAllowFullscreen = m_allowFullscreen;
     m_allowFullscreen = !value.isNull();

third_party/WebKit/Source/core/html/HTMLImageElement.cpp

@@ -267,6 +267,8 @@ void HTMLImageElement::parseAttribute(
     if (!params.newValue.isNull()) {
       SecurityPolicy::referrerPolicyFromStringWithLegacyKeywords(
           params.newValue, &m_referrerPolicy);
+      UseCounter::count(document(),
+                        UseCounter::HTMLImageElementReferrerPolicyAttribute);
     }
   } else {
     HTMLElement::parseAttribute(params);

third_party/WebKit/Source/core/html/HTMLLinkElement.cpp

@@ -82,8 +82,11 @@ void HTMLLinkElement::parseAttribute(
     process();
   } else if (name == referrerpolicyAttr) {
     m_referrerPolicy = ReferrerPolicyDefault;
-    if (!value.isNull())
+    if (!value.isNull()) {
       SecurityPolicy::referrerPolicyFromString(value, &m_referrerPolicy);
+      UseCounter::count(document(),
+                        UseCounter::HTMLLinkElementReferrerPolicyAttribute);
+    }
   } else if (name == sizesAttr) {
     m_sizes->setValue(value);
   } else if (name == mediaAttr) {

tools/metrics/histograms/histograms.xml

@@ -88803,6 +88803,10 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="1751" label="TopNavInSandboxWithPerm"/>
   <int value="1752" label="TopNavInSandboxWithPermButNoGesture"/>
   <int value="1753" label="ReferrerPolicyHeader"/>
+  <int value="1754" label="HTMLAnchorElementReferrerPolicyAttribute"/>
+  <int value="1755" label="HTMLIFrameElementReferrerPolicyAttribute"/>
+  <int value="1756" label="HTMLImageElementReferrerPolicyAttribute"/>
+  <int value="1757" label="HTMLLinkElementReferrerPolicyAttribute"/>
 </enum>
 
 <enum name="FetchRequestMode" type="int">