Bug 539356 - Part 6 - Add compositing paint flashing to BasicLayers. r=roc

gfx/layers/basic/BasicLayerManager.cpp

@@ -20,6 +20,7 @@
 #include "BasicLayersImpl.h"
 #include "BasicThebesLayer.h"
 #include "BasicContainerLayer.h"
+#include "mozilla/Preferences.h"
 
 using namespace mozilla::gfx;
 
@@ -425,6 +426,9 @@ BasicLayerManager::EndTransactionInternal(DrawThebesLayerCallback aCallback,
     }
 
     PaintLayer(mTarget, mRoot, aCallback, aCallbackData, nsnull);
+    if (mWidget) {
+      FlashWidgetUpdateArea(mTarget);
+    }
 
     if (!mTransactionIncomplete) {
       // Clear out target if we have a complete transaction.
@@ -455,6 +459,27 @@ BasicLayerManager::EndTransactionInternal(DrawThebesLayerCallback aCallback,
   return !mTransactionIncomplete;
 }
 
+void
+BasicLayerManager::FlashWidgetUpdateArea(gfxContext *aContext)
+{
+  static bool sWidgetFlashingEnabled;
+  static bool sWidgetFlashingPrefCached = false;
+
+  if (!sWidgetFlashingPrefCached) {
+    sWidgetFlashingPrefCached = true;
+    mozilla::Preferences::AddBoolVarCache(&sWidgetFlashingEnabled,
+                                          "nglayout.debug.widget_update_flashing");
+  }
+
+  if (sWidgetFlashingEnabled) {
+    float r = float(rand()) / RAND_MAX;
+    float g = float(rand()) / RAND_MAX;
+    float b = float(rand()) / RAND_MAX;
+    aContext->SetColor(gfxRGBA(r, g, b, 0.2));
+    aContext->Paint();
+  }
+}
+
 bool
 BasicLayerManager::EndEmptyTransaction()
 {