[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 6985dada5c972a922c69887a6263e1836bb7eaae..eee2e5f8941c4d3c584a680f0cfc369a45993a9b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -61347,6 +61347,17 @@ 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>
@@ -61386,6 +61397,26 @@ 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>