import changes from `dev' branch of rmottola/Arctic-Fox:

- Bug 1161913 - Part 2. Request canvas to push out its next drawn frame instead of pulling it. r=mt (b2ddcd68c3)
- Bug 1161913 - Part 3 - Relax requestFrame ordering guarantee in tests. r=mt (8bc69b9fc4)
- Bug 1176945 - Remove unnecessary hwc reference from gl r=jgilbert (8f1ac06d99)
- spaces and restore XP specific (ac03acf252)
- reinstantiate some gfx log (d7deb9c3bd)
- Bug 1191042 - Use CreateOffscreen for WebGL instead of CreateHeadless. - r=jrmuizel (f98fd02e59)
- space (ad72b4f071)
- Bug 1183085 - Remove EndConstruction() from layer documentation; r=roc (b1ef791fea)
- Bug 771288 - Multiprocess FileHandle support (FileHandle on PBackground); r=baku (f77ab5b9c3)
- Bug 1202788 - Upgrade object_data table to new format (follow-up to bug 871846). r=janv (ea86fd2890)
- Bug 1204183 - Test the object_data upgrade from bug 1202788. r=janv (5a48cfdf17)
- Bug 1198814 - Use StructuredCloneHelper in PromiseWorkerProxy, r=smaug (10e9f33700)
- namespace name (b4feaf8e67)
- Bug 1203561 - Use StructuredCloneHelper in StackScopedCloneData, r=smaug (156525cf32)
- Bug 1209919 - Improving naming and comments in StructuredCloneHelper, r=smaug (f177bca203)
- Bug 1167100 - User originAttribute in ContentPrincipalInfo. r=bholley (340c3d606e)
- Bug 1182197 investigation patch. Log the stack at promise fulfillment on a CCed promise into the crash reporter data. r=dmajor,nsm (376c1bba93)
- Bug 1183907, properly wrappercache worker URL object, r=baku (d71937b9d0)
- Bug 1203463 - URL constructor should support about:blank URI, r=bz (d539b63667)
- Bug 1207496 - Part 4: Remove use of expression closure from services/sync/. r=gps (f1eae787d9)
- Bug 1207496 - Part 3: Remove use of expression closure from services/fxaccounts/. r=markh (f60e64c061)
- Bug 1207496 - Part 2: Remove use of expression closure from services/crypt/. r=mrbkap (ec2738f497)
- Bug 1207496 - Part 1: Remove use of expression closure from services/common/. r=gps (3464407503)
- Bug 1134881 - Sync password timeCreated & timePasswordChanged fields. r=rnewman (96befc78b2)
- adapted version of Bug 753289 - Pre: rename WEAVE_SYNC_PREFS to PREF_SYNC_PREFS_PREFIX. (5987671e36)

dom/indexedDB/IndexedDatabaseManager.cpp

@@ -126,6 +126,7 @@ const uint32_t kDeleteTimeoutMs = 1000;
 
 const char kTestingPref[] = IDB_PREF_BRANCH_ROOT "testing";
 const char kPrefExperimental[] = IDB_PREF_BRANCH_ROOT "experimental";
+const char kPrefFileHandle[] = "dom.fileHandle.enabled";
 
 #define IDB_PREF_LOGGING_BRANCH_ROOT IDB_PREF_BRANCH_ROOT "logging."
 
@@ -146,6 +147,7 @@ Atomic<bool> gInitialized(false);
 Atomic<bool> gClosed(false);
 Atomic<bool> gTestingMode(false);
 Atomic<bool> gExperimentalFeaturesEnabled(false);
+Atomic<bool> gFileHandleEnabled(false);
 
 class DeleteFilesRunnable final
   : public nsIRunnable
@@ -381,6 +383,9 @@ IndexedDatabaseManager::Init()
   Preferences::RegisterCallbackAndCall(AtomicBoolPrefChangedCallback,
                                        kPrefExperimental,
                                        &gExperimentalFeaturesEnabled);
+  Preferences::RegisterCallbackAndCall(AtomicBoolPrefChangedCallback,
+                                       kPrefFileHandle,
+                                       &gFileHandleEnabled);
 
   // By default IndexedDB uses SQLite with PRAGMA synchronous = NORMAL. This
   // guarantees (unlike synchronous = OFF) atomicity and consistency, but not
@@ -446,6 +451,9 @@ IndexedDatabaseManager::Destroy()
   Preferences::UnregisterCallback(AtomicBoolPrefChangedCallback,
                                   kPrefExperimental,
                                   &gExperimentalFeaturesEnabled);
+  Preferences::UnregisterCallback(AtomicBoolPrefChangedCallback,
+                                  kPrefFileHandle,
+                                  &gFileHandleEnabled);
 
   Preferences::UnregisterCallback(LoggingModePrefChangedCallback,
                                   kPrefLoggingDetails);
@@ -742,6 +750,17 @@ IndexedDatabaseManager::ExperimentalFeaturesEnabled()
   return gExperimentalFeaturesEnabled;
 }
 
+// static
+bool
+IndexedDatabaseManager::IsFileHandleEnabled()
+{
+  MOZ_ASSERT(gDBManager,
+             "IsFileHandleEnabled() called before indexedDB has been "
+             "initialized!");
+
+  return gFileHandleEnabled;
+}
+
 already_AddRefed<FileManager>
 IndexedDatabaseManager::GetFileManager(PersistenceType aPersistenceType,
                                        const nsACString& aOrigin,