Bug 1442020 - Ensure neither style nor layout flushes are required when running promiseDocumentFlushed callbacks. r=bz

MozReview-Commit-ID: INGpltVvNmZ

--HG--
extra : rebase_source : 75f51378401f0ca63384a9df52a5e5f04e00bb9d

dom/base/nsGlobalWindowInner.cpp

@@ -7425,7 +7425,7 @@ nsGlobalWindowInner::PromiseDocumentFlushed(PromiseDocumentFlushedCallback& aCal
   UniquePtr<PromiseDocumentFlushedResolver> flushResolver(
     new PromiseDocumentFlushedResolver(resultPromise, aCallback));
 
-  if (!shell->NeedFlush(FlushType::Style)) {
+  if (!shell->NeedStyleFlush() && !shell->NeedLayoutFlush()) {
     flushResolver->Call();
     return resultPromise.forget();
   }
@@ -7520,10 +7520,11 @@ nsGlobalWindowInner::DidRefresh()
   nsIPresShell* shell = mDoc->GetShell();
   MOZ_ASSERT(shell);
 
-  if (shell->NeedStyleFlush() || shell->HasPendingReflow()) {
+  if (shell->NeedStyleFlush() || shell->NeedLayoutFlush()) {
     // By the time our observer fired, something has already invalidated
-    // style and maybe layout. We'll wait until the next refresh driver
-    // tick instead.
+    // style or layout - or perhaps we're still in the middle of a flush that
+    // was interrupted. In either case, we'll wait until the next refresh driver
+    // tick instead and try again.
     rejectionGuard.release();
     return;
   }

dom/base/test/browser_promiseDocumentFlushed.js

@@ -31,7 +31,9 @@ const gWindowUtils = window.QueryInterface(Ci.nsIInterfaceRequestor)
  */
 function assertNoFlushesRequired() {
   Assert.ok(!gWindowUtils.needsFlush(Ci.nsIDOMWindowUtils.FLUSH_STYLE),
-            "No flushes are required.");
+            "No style flushes are required.");
+  Assert.ok(!gWindowUtils.needsFlush(Ci.nsIDOMWindowUtils.FLUSH_LAYOUT),
+            "No layout flushes are required.");
 }
 
 /**
@@ -39,8 +41,10 @@ function assertNoFlushesRequired() {
  * are required.
  */
 function assertFlushesRequired() {
+  Assert.ok(gWindowUtils.needsFlush(Ci.nsIDOMWindowUtils.FLUSH_STYLE),
+            "Style flush required.");
   Assert.ok(gWindowUtils.needsFlush(Ci.nsIDOMWindowUtils.FLUSH_LAYOUT),
-            "Style and layout flushes are required.");
+            "Layout flush required.");
 }
 
 /**

layout/base/nsIPresShell.h

@@ -620,6 +620,12 @@ public:
   }
 
   bool NeedStyleFlush() const { return mNeedStyleFlush; }
+  /**
+   * Returns true if we might need to flush layout, even if we haven't scheduled
+   * one yet (as opposed to HasPendingReflow, which returns true if a flush is
+   * scheduled or will soon be scheduled).
+   */
+  bool NeedLayoutFlush() const { return mNeedLayoutFlush; }
 
   /**
    * Callbacks will be called even if reflow itself fails for
@@ -1638,6 +1644,10 @@ public:
     mIsNeverPainting = aNeverPainting;
   }
 
+  /**
+   * True if a reflow event has been scheduled, or is going to be scheduled
+   * to run in the future.
+   */
   bool HasPendingReflow() const
     { return mObservingLayoutFlushes || mReflowContinueTimer; }