Add sequential dispatching for InitializationRunner

ios/chrome/app/deferred_initialization_runner.h

 // Copyright 2012 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.
 
 #ifndef IOS_CHROME_APP_DEFERRED_INITIALIZATION_RUNNER_H_
 #define IOS_CHROME_APP_DEFERRED_INITIALIZATION_RUNNER_H_
 
 #import <Foundation/Foundation.h>
 
 #include "base/ios/block_types.h"
 
 // A singleton object to run initialization code asynchronously. Blocks are
 // scheduled to be run after a delay. The block is named when added to the
 // singleton so that other code can force a deferred block to be run
 // synchronously if necessary.
 @interface DeferredInitializationRunner : NSObject
 
 // Returns singleton instance.
 + (DeferredInitializationRunner*)sharedInstance;
 
+// Deprecated.
 // Schedules |block| to be run after |delaySeconds| on the current queue.
 // This |block| is stored as |name| so code can force this initialization to
 // be run synchronously if necessary. This method may be called more than
 // once with the same |name| parameter. Any block with the same |name|
 // cancels a previously scheduled block of the same |name| if the block has
 // not been run yet.
 - (void)runBlockNamed:(NSString*)name
                 after:(NSTimeInterval)delaySeconds
                 block:(ProceduralBlock)block;
 
+// Adds |block| to a block queue containing all block not run. All blocks in the
+// queue are run sequentially with a small delay between each block.
+// If the queue is empty |block| is run after a small delay.
+// This |block| is stored as |name| so code can force this initialization to
+// be run synchronously if necessary. This method may be called more than
+// once with the same |name| parameter. Any block with the same |name|
+// cancels a previously scheduled block of the same |name| if the block has
+// not been run yet.
+- (void)enqueueBlockNamed:(NSString*)name block:(ProceduralBlock)block;
+
 // Looks up a previously scheduled block of |name|. If block has not been
 // run yet, run it synchronously now.
 - (void)runBlockIfNecessary:(NSString*)name;
 
 // Cancels a previously scheduled block of |name|. This is a no-op if the
 // block has already been executed.
 - (void)cancelBlockNamed:(NSString*)name;
 
 // Number of blocks that have been registered but not executed yet.
 // Exposed for testing.
 @property(nonatomic, readonly) NSUInteger numberOfBlocksRemaining;
 
+// Time interval between two blocks. Default value is 200ms.
+@property(nonatomic) NSTimeInterval delayBetweenBlocks;
+
+// Time interval before running the first block. Default value is 3s.
+@property(nonatomic) NSTimeInterval delayBeforeFirstBlocks;

[pkl (ping after 24h if needed), 2016/08/19 23:48:20]

Shouldn't this be singular, i.e. delayBeforeFirstBlock?

I think you should mention here that the value for this must be set *before* the
first call to -enqueueBlockNamed:. Once enqueue is called, setting this value
has no effect. Since DeferredInitializationRunner is a singleton class, this
makes the first call to +sharedInstance the one that gets the "first block"
delay. This API feels a bit "strange".

Is it really necessary to expose -delayBetweenBlocks and -delayBeforeFirstBlock
as part of this API? Is it really being used (other than for unit tests)?

[gambard, 2016/09/13 09:59:03]

You are right. This makes little sense as public API.
I have put it into category for testing only.

+
 @end
 
 #endif  // IOS_CHROME_APP_DEFERRED_INITIALIZATION_RUNNER_H_