Implement initialization for GDataCache to use in-memory metadata for tests.

chrome/browser/chromeos/gdata/gdata_cache_metadata.h

Index: chrome/browser/chromeos/gdata/gdata_cache_metadata.h
diff --git a/chrome/browser/chromeos/gdata/gdata_cache_metadata.h b/chrome/browser/chromeos/gdata/gdata_cache_metadata.h
index d6bebd516716b2ec5a52dbe65ac710e1949ac9e5..281497a7bfda8414f4622e598fff48178d031a6f 100644
--- a/chrome/browser/chromeos/gdata/gdata_cache_metadata.h
+++ b/chrome/browser/chromeos/gdata/gdata_cache_metadata.h
@@ -31,14 +31,15 @@ class GDataCacheMetadata {
 
   virtual ~GDataCacheMetadata();
 
-  // |pool| and |sequence_token| are used to assert that the functions are
-  // called on the right sequenced worker pool with the right sequence token.
-  //
-  // For testing, the thread assertion can be disabled by passing NULL and
-  // the default value of SequenceToken.
+  // Creates GDataCacheMetadata instance.
   static scoped_ptr<GDataCacheMetadata> CreateGDataCacheMetadata(
       base::SequencedTaskRunner* blocking_task_runner);
 
+  // Creates GDataCacheMetadata instance. This uses FakeGDataCacheMetadata,
+  // which is an in-memory implmentation and faster than GDataCacheMetadataDB.
+  static scoped_ptr<GDataCacheMetadata> CreateGDataCacheMetadataForTesting(
+      base::SequencedTaskRunner* blocking_task_runner);
+
   // Initialize the cache metadata store.
   virtual void Initialize(const std::vector<FilePath>& cache_paths) = 0;
   // Adds a new cache entry corresponding to |resource_id| if it doesn't