Fixed crashes in CrNetEnvironment::ConfigureSdchOnNetworkThread()

ios/crnet/CrNet.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import <Foundation/Foundation.h>
 
 // A block, that takes a request, and returns YES if the request should
 // be handled.
 typedef BOOL(^RequestFilterBlock)(NSURLRequest *request);
 
@@ skipping 32 matching lines @@
 + (void)setPartialUserAgent:(NSString *)userAgent;
 
 // Set the block used to determine whether or not CrNet should handle the
 // request. If this is not set, CrNet will handle all requests.
 // Must not be called while requests are in progress. This method can be called
 // either before or after |install|.
 + (void)setRequestFilterBlock:(RequestFilterBlock)block;
 
 // Installs CrNet. Once installed, CrNet intercepts and handles all
 // NSURLConnection and NSURLRequests issued by the app, including UIWebView page
-// loads.
+// loads. It is recommended to call this method on the application main thread.
+// If the method is called on any thread other than the main one, the method
+// will internally try to execute synchronously using the main GCD queue.
+// Please make sure that the main thread is not blocked by a job
+// that calls this method; otherwise, a deadlock can occur.
 + (void)install;
 
 // Installs CrNet into an NSURLSession, passed in by the caller. Note that this
 // NSURLSession will share settings with the sharedSession, which the |install|
 // method installs CrNet into. This method must be called after |install|.
 + (void)installIntoSessionConfiguration:(NSURLSessionConfiguration*)config;
 
 // Installs CrNet. This function is a deprecated shortcut for:
 //    [CrNet setPartialUserAgent:userAgent];
 //    [CrNet install];
@@ skipping 44 matching lines @@
 
 // Returns the full user-agent that the stack uses.
 // This is the exact string servers will see.
 + (NSString *)userAgent;
 
 // Clears CrNet's http cache. The supplied callback, if not nil, is run on an
 // unspecified thread.
 + (void)clearCacheWithCompletionCallback:(ClearCacheCallback)completionBlock;
 
 @end