Add sys trace for WebViewContentsClientAdapter

In the startup trace log from perf dashboard, there is some empty space
(~8 ms) between WebViewChromiumFactoryProvider.startYourEngines() and
WebViewChromium.ContentSettingsAdapter().

https://chromeperf.appspot.com/report?sid=5ae87c41efb3d436419396e0551577a6e5bb1dc9544c55bf0e2881db28ed54be

This is not reproducible in a local trace benchmark run.

checkThread() and WebViewContentsClientAdapter's constructor seem to be
the only methods that are called in between, but checkThread() doesn't
look like a culprit, so adding trace to the constructor to verify it.

BUG=817644

Change-Id: I80da1b0ea74e2c7f005398a0a54bde1d38296222
Reviewed-on: https://chromium-review.googlesource.com/1038225Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Changwan Ryu <changwan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555227}

android_webview/glue/java/src/com/android/webview/chromium/WebViewContentsClientAdapter.java

@@ -52,6 +52,7 @@ import org.chromium.android_webview.AwWebResourceResponse;
 import org.chromium.android_webview.JsPromptResultReceiver;
 import org.chromium.android_webview.JsResultReceiver;
 import org.chromium.android_webview.SafeBrowsingAction;
+import org.chromium.android_webview.ScopedSysTraceEvent;
 import org.chromium.android_webview.permission.AwPermissionRequest;
 import org.chromium.android_webview.permission.Resource;
 import org.chromium.base.Callback;
@@ -142,35 +143,39 @@ class WebViewContentsClientAdapter extends AwContentsClient {
         mContext = context;
         mWebView = webView;
         mWebViewDelegate = webViewDelegate;
-        mSupportLibClient = new SupportLibWebViewContentsClientAdapter();
-        setWebViewClient(null);
+        try (ScopedSysTraceEvent event =
+                        ScopedSysTraceEvent.scoped("WebViewContentsClientAdapter.constructor")) {
+            mSupportLibClient = new SupportLibWebViewContentsClientAdapter();
+            setWebViewClient(null);
 
-        mUiThreadHandler = new Handler() {
-            @Override
-            public void handleMessage(Message msg) {
-                switch (msg.what) {
-                    case NEW_WEBVIEW_CREATED:
-                        WebView.WebViewTransport t = (WebView.WebViewTransport) msg.obj;
-                        WebView newWebView = t.getWebView();
-                        if (newWebView == mWebView) {
-                            throw new IllegalArgumentException(
-                                    "Parent WebView cannot host it's own popup window. Please "
-                                    + "use WebSettings.setSupportMultipleWindows(false)");
-                        }
-
-                        if (newWebView != null && newWebView.copyBackForwardList().getSize() != 0) {
-                            throw new IllegalArgumentException(
-                                    "New WebView for popup window must not have been previously "
-                                    + "navigated.");
-                        }
-
-                        WebViewChromium.completeWindowCreation(mWebView, newWebView);
-                        break;
-                    default:
-                        throw new IllegalStateException();
+            mUiThreadHandler = new Handler() {
+                @Override
+                public void handleMessage(Message msg) {
+                    switch (msg.what) {
+                        case NEW_WEBVIEW_CREATED:
+                            WebView.WebViewTransport t = (WebView.WebViewTransport) msg.obj;
+                            WebView newWebView = t.getWebView();
+                            if (newWebView == mWebView) {
+                                throw new IllegalArgumentException(
+                                        "Parent WebView cannot host it's own popup window. Please "
+                                        + "use WebSettings.setSupportMultipleWindows(false)");
+                            }
+
+                            if (newWebView != null
+                                    && newWebView.copyBackForwardList().getSize() != 0) {
+                                throw new IllegalArgumentException(
+                                        "New WebView for popup window must not have been "
+                                        + " previously navigated.");
+                            }
+
+                            WebViewChromium.completeWindowCreation(mWebView, newWebView);
+                            break;
+                        default:
+                            throw new IllegalStateException();
+                    }
                 }
-            }
-        };
+            };
+        }
     }
 
     void setWebViewClient(WebViewClient client) {