[Cronet] Implement methods to get response headers in HttpURLConnection.

components/cronet/android/java/src/org/chromium/net/urlconnection/CronetHttpURLConnection.java

Index: components/cronet/android/java/src/org/chromium/net/urlconnection/CronetHttpURLConnection.java
diff --git a/components/cronet/android/java/src/org/chromium/net/urlconnection/CronetHttpURLConnection.java b/components/cronet/android/java/src/org/chromium/net/urlconnection/CronetHttpURLConnection.java
index 9c308ae1f5fba209df0e7c83a9db181bbcb233e6..0d965000c72e1b844a83fc29c1e80cc6aac7d03b 100644
--- a/components/cronet/android/java/src/org/chromium/net/urlconnection/CronetHttpURLConnection.java
+++ b/components/cronet/android/java/src/org/chromium/net/urlconnection/CronetHttpURLConnection.java
@@ -114,6 +114,77 @@ public class CronetHttpURLConnection extends HttpURLConnection {
     }
 
     /**
+     * Returns an unmodifiable map of the response-header fields and values.
+     */
+    @Override
+    public Map<String, List<String>> getHeaderFields() {
+        try {
+            connect();
+        } catch (IOException e) {
+            return Collections.emptyMap();
+        }
+        return mResponseInfo.getAllHeaders();
+    }
+
+    /**
+     * Returns the value of the named header field. If called on a connection
+     * that sets the same header multiple times with possibly different values,
+     * only the last value is returned.
+     */
+    @Override
+    public final String getHeaderField(String fieldName) {

[mef, 2015/01/30 16:22:52]

Is implementation of getHeaderField enough to support
getHeaderField{Date|Int|Long} or do we need to implement those explicitly?

[xunjieli, 2015/01/30 18:22:58]

We can rely on the default implementations which reuse
getHeaderField/getHeaderFieldKey. OkHttp does the same.

+        try {
+            connect();
+        } catch (IOException e) {
+            return null;
+        }
+        Map<String, List<String>> map = mResponseInfo.getAllHeaders();
+        if (!map.containsKey(fieldName)) {
+            return null;
+        }
+        List<String> values = map.get(fieldName);
+        return values.get(values.size() - 1);
+    }
+
+    /**
+     * Returns the name of the header field at the given position pos, or null
+     * if there are fewer than pos fields.
+     */
+    @Override
+    public final String getHeaderFieldKey(int pos) {
+        try {
+            connect();
+        } catch (IOException e) {
+            return null;
+        }
+        List<Pair<String, String>> headers =
+                mResponseInfo.getAllHeadersAsList();
+        if (pos >= headers.size()) {
+            return null;
+        }
+        return headers.get(pos).first;
+    }
+
+    /**
+     * Returns the header value at the field position pos or null if the header
+     * has fewer than pos fields.
+     */
+    @Override
+    public final String getHeaderField(int pos) {
+        try {

[mef, 2015/01/30 16:22:52]

nit: maybe factor out most of getHeaderField{Key} into something like
getHeaderFieldPair?

[xunjieli, 2015/01/30 18:22:58]

Done.

+            connect();
+        } catch (IOException e) {
+            return null;
+        }
+        List<Pair<String, String>> headers =
+                mResponseInfo.getAllHeadersAsList();
+        if (pos >= headers.size()) {
+            return null;
+        }
+        return headers.get(pos).second;
+    }
+
+    /**
      * Returns an InputStream for reading data from the resource pointed by this
      * URLConnection.
      * @throws FileNotFoundException if http response code is equal or greater