Return detailed reason of invalid proxy settings

Make Proxy.validate() return valid/invalid int code, instead of throwing
exceptions. If invalid, detailed reason code is returned (currently for
Settings UI use).

bug: 13248097
Change-Id: Ic68d03f666f1cd63667afc311de7dc370d233901
diff --git a/core/java/android/net/ProxyProperties.java b/core/java/android/net/ProxyProperties.java
index 54fc01d..50f45e8 100644
--- a/core/java/android/net/ProxyProperties.java
+++ b/core/java/android/net/ProxyProperties.java
@@ -140,13 +140,9 @@
 
     public boolean isValid() {
         if (!TextUtils.isEmpty(mPacFileUrl)) return true;
-        try {
-            Proxy.validate(mHost == null ? "" : mHost, mPort == 0 ? "" : Integer.toString(mPort),
-                    mExclusionList == null ? "" : mExclusionList);
-        } catch (IllegalArgumentException e) {
-            return false;
-        }
-        return true;
+        return Proxy.PROXY_VALID == Proxy.validate(mHost == null ? "" : mHost,
+                                                mPort == 0 ? "" : Integer.toString(mPort),
+                                                mExclusionList == null ? "" : mExclusionList);
     }
 
     public java.net.Proxy makeProxy() {