IndexedDB: Rework usage metric.

Switch from counting usage of the indexedDB property on the global
object to counting indexedDB.open(). The former can get triggered by
code that walks all global properties, while the latter is real
IndexedDB usage.

Change-Id: I36d003321ea0ca24a07034cbce89c33c39c67959
Reviewed-on: https://chromium-review.googlesource.com/1170392Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582534}

third_party/blink/public/platform/web_feature.mojom

@@ -17,7 +17,6 @@ enum WebFeature {
   kOBSOLETE_PageDestruction = 0,
   kWorkerStart = 4,
   kSharedWorkerStart = 5,
-  kUnprefixedIndexedDB = 9,
   kOpenWebDatabase = 10,
   kUnprefixedRequestAnimationFrame = 13,
   kPrefixedRequestAnimationFrame = 14,
@@ -1981,6 +1980,7 @@ enum WebFeature {
   kPPAPIWebSocket = 2524,
   kV8MediaStreamTrack_ContentHint_AttributeGetter = 2525,
   kV8MediaStreamTrack_ContentHint_AttributeSetter = 2526,
+  kV8IDBFactory_Open_Method = 2527,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

third_party/blink/renderer/modules/indexeddb/idb_factory.idl

@@ -28,7 +28,12 @@
 [
     Exposed=(Window,Worker)
 ] interface IDBFactory {
-    [NewObject, CallWith=ScriptState, RaisesException] IDBOpenDBRequest open(DOMString name,
+    [
+        NewObject,
+        CallWith=ScriptState,
+        Measure,
+        RaisesException
+    ] IDBOpenDBRequest open(DOMString name,
                             optional [EnforceRange] unsigned long long version);
     [NewObject, CallWith=ScriptState, RaisesException] IDBOpenDBRequest deleteDatabase(DOMString name);
 

third_party/blink/renderer/modules/indexeddb/window_indexed_database.idl

@@ -27,5 +27,5 @@
 [
     ImplementedAs=GlobalIndexedDB
 ] partial interface Window {
-    [MeasureAs=UnprefixedIndexedDB] readonly attribute IDBFactory indexedDB;
+    readonly attribute IDBFactory indexedDB;
 };

tools/metrics/histograms/enums.xml

@@ -19581,6 +19581,7 @@ Called by update_net_error_codes.py.-->
   <int value="2524" label="PPAPIWebSocket"/>
   <int value="2525" label="V8MediaStreamTrack_ContentHint_AttributeGetter"/>
   <int value="2526" label="V8MediaStreamTrack_ContentHint_AttributeSetter"/>
+  <int value="2527" label="V8IDBFactory_Open_Method"/>
 </enum>
 
 <enum name="FeedbackSource">