Remove untrusted event deprecation warning.

The feature now has shipped and we don't need the warning anymore.
The runtime setting is still available since one unit test still uses it.
I need to get some cycles to see if that can be removed.

BUG=520519

Review-Url: https://codereview.chromium.org/2375583003
Cr-Commit-Position: refs/heads/master@{#421351}

third_party/WebKit/Source/core/events/EventDispatcher.cpp

@@ -253,8 +253,6 @@ inline void EventDispatcher::dispatchEventPostProcess(EventDispatchHandlingState
                     break;
             }
         }
-        if (m_event->defaultHandled() && !m_event->isTrusted() && !isClick)
-            Deprecation::countDeprecation(m_node->document(), UseCounter::UntrustedEventDefaultHandled);
     }
 
     // Track the usage of sending a mousedown event to a select element to force

third_party/WebKit/Source/core/frame/Deprecation.cpp

@@ -15,7 +15,6 @@
 namespace {
 
 enum Milestone {
-    M53,
     M55,
     M56,
     M57,
@@ -29,8 +28,6 @@ const char* milestoneString(Milestone milestone)
     // https://www.chromium.org/developers/calendar
 
     switch (milestone) {
-    case M53:
-        return "M53, around September 2016";
     case M55:
         return "M55, around December 2016";
     case M56:
@@ -362,9 +359,6 @@ String Deprecation::deprecationMessage(UseCounter::Feature feature)
     case UseCounter::EncryptedMediaAllSelectedContentTypesMissingCodecs:
         return String::format("EME requires that contentType strings accepted by requestMediaKeySystemAccess() include codecs. Non-standard support for contentType strings without codecs will be removed in %s. Please specify the desired codec(s) as part of the contentType.", milestoneString(M56));
 
-    case UseCounter::UntrustedEventDefaultHandled:
-        return String::format("A DOM event generated from JavaScript has triggered a default action inside the browser. This behavior is non-standard and will be removed in %s. See https://www.chromestatus.com/features/5718803933560832 for more details.", milestoneString(M53));
-
     case UseCounter::TouchStartUserGestureUtilized:
         return willBeRemoved("Performing operations that require explicit user interaction on touchstart events", M55, "5649871251963904");
 

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

@@ -1113,7 +1113,6 @@ public:
         DurableStoragePersist = 1369,
         DurableStoragePersisted = 1370,
         DurableStorageEstimate = 1371,
-        UntrustedEventDefaultHandled = 1372,
         CSSDeepCombinatorAndShadow = 1375,
         OpacityWithPreserve3DQuirk = 1376,
         CSSSelectorPseudoReadOnly = 1377,