Add sequential dispatching for InitializationRunner

ios/chrome/app/deferred_initialization_runner.h

Index: ios/chrome/app/deferred_initialization_runner.h
diff --git a/ios/chrome/app/deferred_initialization_runner.h b/ios/chrome/app/deferred_initialization_runner.h
index e1bd59ce5e9006bb2fed80ffb1fd0202fc852000..336fa03be801201ac8697c71f5e4d501c6b2170a 100644
--- a/ios/chrome/app/deferred_initialization_runner.h
+++ b/ios/chrome/app/deferred_initialization_runner.h
@@ -18,6 +18,7 @@
 // Returns singleton instance.
 + (DeferredInitializationRunner*)sharedInstance;
 
+// Deprecated, use |enqueueBlockNamed:block:| instead.
 // 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
@@ -28,6 +29,12 @@
                 after:(NSTimeInterval)delaySeconds
                 block:(ProceduralBlock)block;
 
+// Stores |block| under |name| to a queue of blocks to run. All blocks are run
+// sequentially with a small delay before the first block and between each
+// successive block. If a block is already registered under |name|, it is
+// replaced with |block| unless it has already been run.
+- (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;
@@ -42,4 +49,15 @@
 
 @end
 
+@interface DeferredInitializationRunner (ExposedForTesting)
+
+// Time interval between two blocks. Default value is 200ms.
+@property(nonatomic, assign) NSTimeInterval delayBetweenBlocks;
+
+// Time interval before running the first block. To override default value of
+// 3s, set this property before the first call to |-enqueueBlockNamed:block:|.
+@property(nonatomic, assign) NSTimeInterval delayBeforeFirstBlock;
+
+@end
+
 #endif  // IOS_CHROME_APP_DEFERRED_INITIALIZATION_RUNNER_H_