bindings: Improves the speed perf of EventTarget.dispatchEvent.

Introduces a hack to recover the speed performance of
EventTarget.dispatchEvent.  The code looks like close to the one before
http://crrev.com/1417023006 .

BUG=564407, 509936

Review URL: https://codereview.chromium.org/1494803003

Cr-Commit-Position: refs/heads/master@{#362937}

third_party/WebKit/Source/bindings/templates/methods.cpp

@@ -28,12 +28,27 @@ static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}(const
     {% endif %}
     {# Security checks #}
     {% if method.is_check_security_for_receiver %}
+    {% if interface_name == 'EventTarget' %}
+    // Performance hack for EventTarget.  Checking whether it's a Window or not
+    // prior to the call to BindingSecurity::shouldAllowAccessTo increases 30%
+    // of speed performance on Android Nexus 7 as of Dec 2016.  ALWAYS_INLINE
+    // didn't work in this case.
+    if (LocalDOMWindow* window = impl->toDOMWindow()) {
+        if (!BindingSecurity::shouldAllowAccessTo(info.GetIsolate(), callingDOMWindow(info.GetIsolate()), window, exceptionState)) {
+            {% if not method.returns_promise %}
+            exceptionState.throwIfNeeded();
+            {% endif %}
+            return;
+        }
+    }
+    {% else %}{# interface_name == 'EventTarget' #}
     if (!BindingSecurity::shouldAllowAccessTo(info.GetIsolate(), callingDOMWindow(info.GetIsolate()), impl, exceptionState)) {
         {% if not method.returns_promise %}
         exceptionState.throwIfNeeded();
         {% endif %}
         return;
     }
+    {% endif %}{# interface_name == 'EventTarget' #}
     {% endif %}
     {% if method.is_check_security_for_return_value %}
     if (!BindingSecurity::shouldAllowAccessTo(info.GetIsolate(), callingDOMWindow(info.GetIsolate()), {{method.cpp_value}}, exceptionState)) {