Bug 1730456 - InitPlatformFontList should reframe. r=jfkthame

I don't know why it didn't broadcast the reflow request to child
processes... Perhaps it doesn't have to?

Differential Revision: https://phabricator.services.mozilla.com/D126128

gfx/thebes/gfxPlatform.cpp

@@ -2215,7 +2215,8 @@ void gfxPlatform::FlushFontAndWordCaches() {
 }
 
 /* static */
-void gfxPlatform::ForceGlobalReflow(NeedsReframe aNeedsReframe) {
+void gfxPlatform::ForceGlobalReflow(NeedsReframe aNeedsReframe,
+                                    BroadcastToChildren aBroadcastToChildren) {
   MOZ_ASSERT(NS_IsMainThread());
   const bool reframe = aNeedsReframe == NeedsReframe::Yes;
   // Send a notification that will be observed by PresShells in this process
@@ -2224,7 +2225,8 @@ void gfxPlatform::ForceGlobalReflow(NeedsReframe aNeedsReframe) {
     char16_t needsReframe[] = {char16_t(reframe), 0};
     obs->NotifyObservers(nullptr, "font-info-updated", needsReframe);
   }
-  if (XRE_IsParentProcess()) {
+  if (XRE_IsParentProcess() &&
+      aBroadcastToChildren == BroadcastToChildren::Yes) {
     // Propagate the change to child processes.
     for (auto* process :
          dom::ContentParent::AllProcesses(dom::ContentParent::eLive)) {

gfx/thebes/gfxPlatform.h

@@ -607,13 +607,19 @@ class gfxPlatform : public mozilla::layers::MemoryPressureListener {
   int32_t GetBidiNumeralOption();
 
   /**
-   * This is a bit ugly, but useful... force all presContexts to reflow,
-   * by toggling a preference that they observe. This is used when
-   * something about platform settings changes that might have an effect
-   * on layout, such as font rendering settings that influence metrics.
+   * Force all presContexts to reflow (and reframe if needed).
+   *
+   * This is used when something about platform settings changes that might have
+   * an effect on layout, such as font rendering settings that influence
+   * metrics, or installed fonts.
+   *
+   * By default it also broadcast it to child processes, but some callers might
+   * not need it if they implement their own notification.
    */
   enum class NeedsReframe : bool { No, Yes };
-  static void ForceGlobalReflow(NeedsReframe);
+  enum class BroadcastToChildren : bool { No, Yes };
+  static void ForceGlobalReflow(NeedsReframe,
+                                BroadcastToChildren = BroadcastToChildren::Yes);
 
   static void FlushFontAndWordCaches();
 

gfx/thebes/gfxPlatformFontList.cpp

@@ -471,22 +471,17 @@ bool gfxPlatformFontList::InitFontList() {
 
     gfxPlatform::PurgeSkiaFontCache();
 
+    // There's no need to broadcast this reflow request to child processes, as
+    // ContentParent::NotifyUpdatedFonts deals with it by re-entering into this
+    // function on child processes.
     if (NS_IsMainThread()) {
-      nsCOMPtr<nsIObserverService> obs =
-          mozilla::services::GetObserverService();
-      if (obs) {
-        // Notify any current presContexts that fonts are being updated, so
-        // existing caches will no longer be valid.
-        obs->NotifyObservers(nullptr, "font-info-updated", nullptr);
-      }
+      gfxPlatform::ForceGlobalReflow(gfxPlatform::NeedsReframe::Yes,
+                                     gfxPlatform::BroadcastToChildren::No);
     } else {
       NS_DispatchToMainThread(
           NS_NewRunnableFunction("font-info-updated notification callback", [] {
-            nsCOMPtr<nsIObserverService> obs =
-                mozilla::services::GetObserverService();
-            if (obs) {
-              obs->NotifyObservers(nullptr, "font-info-updated", nullptr);
-            }
+            gfxPlatform::ForceGlobalReflow(gfxPlatform::NeedsReframe::Yes,
+                                           gfxPlatform::BroadcastToChildren::No);
           }));
     }