Custom Tabs: fix misnamed page load metrics.

The REPONSE_START and RESPONSE_END page load metrics reported from
custom tabs should be named SEND_START and SEND_END to be consistent
with the navigation timing API.

Bug: 
Change-Id: Id6d5de07d1c3748ed2921fc94bfa7ac8dcf72252
Reviewed-on: https://chromium-review.googlesource.com/832481Reviewed-by: Benoit L <lizeb@chromium.org>
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Cr-Commit-Position: refs/heads/master@{#525297}

chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java

@@ -203,8 +203,8 @@ public class CustomTabActivity extends ChromeActivity {
             args.putLong(PageLoadMetrics.CONNECT_START, connectStartMs);
             args.putLong(PageLoadMetrics.CONNECT_END, connectEndMs);
             args.putLong(PageLoadMetrics.REQUEST_START, requestStartMs);
-            args.putLong(PageLoadMetrics.RESPONSE_START, sendStartMs);
-            args.putLong(PageLoadMetrics.RESPONSE_END, sendEndMs);
+            args.putLong(PageLoadMetrics.SEND_START, sendStartMs);
+            args.putLong(PageLoadMetrics.SEND_END, sendEndMs);
             mConnection.notifyPageLoadMetrics(mSession, args);
         }
     }

chrome/android/java/src/org/chromium/chrome/browser/metrics/PageLoadMetrics.java

@@ -24,8 +24,8 @@ public class PageLoadMetrics {
     public static final String CONNECT_START = "connectStart";
     public static final String CONNECT_END = "connectEnd";
     public static final String REQUEST_START = "requestStart";
-    public static final String RESPONSE_START = "responseStart";
-    public static final String RESPONSE_END = "responseEnd";
+    public static final String SEND_START = "sendStart";
+    public static final String SEND_END = "sendEnd";
     public static final String EFFECTIVE_CONNECTION_TYPE = "effectiveConnectionType";
     public static final String HTTP_RTT = "httpRtt";
     public static final String TRANSPORT_RTT = "transportRtt";