[cronet] make startNetLogToFile write to correct file

components/cronet/ios/Cronet.mm

Index: components/cronet/ios/Cronet.mm
diff --git a/components/cronet/ios/Cronet.mm b/components/cronet/ios/Cronet.mm
index 1fd0c3d99e0d12635e12cd4058532fee2b54c16f..bf6fd445fe398c4e16fbffc1b15b432cdd9f1ad4 100644
--- a/components/cronet/ios/Cronet.mm
+++ b/components/cronet/ios/Cronet.mm
@@ -230,10 +230,19 @@ class CronetHttpProtocolHandlerDelegate
   config.protocolClasses = @[ [CRNPauseableHTTPProtocolHandler class] ];
 }
 
-+ (void)startNetLogToFile:(NSString*)fileName logBytes:(BOOL)logBytes {
++ (NSString*)netLogPath:(NSString*)fileName {

[mef, 2016/12/09 18:30:40]

So, fileName can never be an absolute path, right?

[lilyhoughton, 2016/12/09 19:42:50]

Yeah

+  return [[[[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory
+                                                   inDomains:NSUserDomainMask]
+      lastObject] URLByAppendingPathComponent:fileName] path];
+}
+
++ (BOOL)startNetLogToFile:(NSString*)fileName logBytes:(BOOL)logBytes {
   if (gChromeNet.Get().get() && [fileName length]) {
-    gChromeNet.Get()->StartNetLog([fileName UTF8String], logBytes);
+    return gChromeNet.Get()->StartNetLog(
+        base::SysNSStringToUTF8([self netLogPath:fileName]), logBytes);
   }
+
+  return NO;
 }
 
 + (void)stopNetLog {