[BlobStorage] BlobMemoryController & tests

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index b7a62beac2293ee572cd2b68cc4027b3b675d700..76e0cdc0d260a33541ed57736e572f7078c09274 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -60261,6 +60261,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Storage.Blob.CreateDirectoryResult" enum="PlatformFileError">
+  <owner>dmurph@chromium.org</owner>
+  <summary>
+    Recorded when we create the blob storage directory for the blob storage
+    system. When we need to write blob data to files, we create this directory
+    if it doesn't exist. We write blob data to files when either we have a new
+    blob that's larger than our memory limit, or we're approaching our in-memory
+    limit for blob storage.
+  </summary>
+</histogram>
+
 <histogram name="Storage.Blob.ExceededMemory" enum="Boolean">
   <owner>dmurph@chromium.org</owner>
   <obsolete>
@@ -60300,6 +60311,26 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Storage.Blob.PageFileSize" units="KB">
+  <owner>dmurph@chromium.org</owner>
+  <summary>
+    Size of a page file created for blob data by the blob storage system.
+    Recorded before we create the file and write the blob items. We page blob
+    data to files when we get close to our maximum blob memory usage.
+  </summary>
+</histogram>
+
+<histogram name="Storage.Blob.PagingDisabled" enum="PlatformFileError">
+  <owner>dmurph@chromium.org</owner>
+  <summary>
+    Recorded when we disable paging blobs to file in the blob storage system.
+    This occurs when we experience a filesystem error during writing blob data
+    to disk. We write blob data to files when either we have a new blob that's
+    larger than our memory limit, or we're approaching our in-memory limit for
+    blob storage. The relevant error is recorded here.
+  </summary>
+</histogram>
+
 <histogram name="Storage.Blob.RendererFileSeekFailed" enum="Boolean">
   <owner>dmurph@chromium.org</owner>
   <summary>