diff --git a/gfx/layers/client/ClientLayerManager.cpp b/gfx/layers/client/ClientLayerManager.cpp
index 11368434416..6e495ebf917 100644
--- a/gfx/layers/client/ClientLayerManager.cpp
+++ b/gfx/layers/client/ClientLayerManager.cpp
@@ -164,6 +164,7 @@ ClientLayerManager::BeginTransactionWithTarget(gfxContext* aTarget)
   // If this is a new paint, increment the paint sequence number.
   if (!mIsRepeatTransaction) {
     ++mPaintSequenceNumber;
+    mApzTestData.StartNewPaint(mPaintSequenceNumber);
   }
 }
 
diff --git a/gfx/layers/client/ClientLayerManager.h b/gfx/layers/client/ClientLayerManager.h
index 9eb36aff101..cfc3e5c88eb 100644
--- a/gfx/layers/client/ClientLayerManager.h
+++ b/gfx/layers/client/ClientLayerManager.h
@@ -16,6 +16,7 @@
 #include "mozilla/layers/CompositorTypes.h"
 #include "mozilla/layers/LayersTypes.h"  // for BufferMode, LayersBackend, etc
 #include "mozilla/layers/ShadowLayers.h"  // for ShadowLayerForwarder, etc
+#include "mozilla/layers/APZTestData.h" // for APZTestData
 #include "nsAutoPtr.h"                  // for nsRefPtr
 #include "nsCOMPtr.h"                   // for already_AddRefed
 #include "nsDebug.h"                    // for NS_ABORT_IF_FALSE
@@ -172,6 +173,31 @@ public:
    return (GetTextureFactoryIdentifier().mSupportedBlendModes & aMixBlendModes) == aMixBlendModes;
   }
 
+  // Log APZ test data for the current paint. We supply the paint sequence
+  // number ourselves, and take care of calling APZTestData::StartNewPaint()
+  // when a new paint is started.
+  void LogTestDataForCurrentPaint(FrameMetrics::ViewID aScrollId,
+                                  const std::string& aKey,
+                                  const std::string& aValue)
+  {
+    mApzTestData.LogTestDataForPaint(mPaintSequenceNumber, aScrollId, aKey, aValue);
+  }
+
+  // Log APZ test data for a repaint request. The sequence number must be
+  // passed in from outside, and APZTestData::StartNewRepaintRequest() needs
+  // to be called from the outside as well when a new repaint request is started.
+  void StartNewRepaintRequest(SequenceNumber aSequenceNumber)
+  {
+    mApzTestData.StartNewRepaintRequest(aSequenceNumber);
+  }
+  void LogTestDataForRepaintRequest(SequenceNumber aSequenceNumber,
+                                    FrameMetrics::ViewID aScrollId,
+                                    const std::string& aKey,
+                                    const std::string& aValue)
+  {
+    mApzTestData.LogTestDataForRepaintRequest(aSequenceNumber, aScrollId, aKey, aValue);
+  }
+
 protected:
   enum TransactionPhase {
     PHASE_NONE, PHASE_CONSTRUCTION, PHASE_DRAWING, PHASE_FORWARD
@@ -236,6 +262,8 @@ private:
   // Incremented in BeginTransaction(), but not for repeat transactions.
   uint32_t mPaintSequenceNumber;
 
+  APZTestData mApzTestData;
+
   RefPtr<ShadowLayerForwarder> mForwarder;
   nsAutoTArray<RefPtr<TextureClientPool>,2> mTexturePools;
   nsAutoTArray<dom::OverfillCallback*,0> mOverfillCallbacks;
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index a1ed129e149..b31ee752a52 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -77,6 +77,7 @@
 #include "mozilla/LookAndFeel.h"
 #include "UnitTransforms.h"
 #include "TiledLayerBuffer.h" // For TILEDLAYERBUFFER_TILE_SIZE
+#include "ClientLayerManager.h"
 
 #include "mozilla/Preferences.h"
 
@@ -6514,7 +6515,21 @@ nsLayoutUtils::WantSubAPZC()
    }
 #endif
    return wantSubAPZC;
- }
+}
+
+/* static */ void
+nsLayoutUtils::LogTestDataForPaint(nsIPresShell* aPresShell,
+                                   ViewID aScrollId,
+                                   const std::string& aKey,
+                                   const std::string& aValue)
+{
+  nsRefPtr<LayerManager> lm = aPresShell->GetPresContext()->GetRootPresContext()
+      ->GetPresShell()->GetLayerManager();
+  if (lm && lm->GetBackendType() == LayersBackend::LAYERS_CLIENT) {
+    static_cast<ClientLayerManager*>(lm.get())->LogTestDataForCurrentPaint(aScrollId, aKey, aValue);
+  }
+}
+
 
 nsLayoutUtils::SurfaceFromElementResult::SurfaceFromElementResult()
   // Use safe default values here
diff --git a/layout/base/nsLayoutUtils.h b/layout/base/nsLayoutUtils.h
index 2839fe2c0aa..29e1ad988de 100644
--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -26,6 +26,7 @@
 #include "imgIContainer.h"
 #include "mozilla/gfx/2D.h"
 #include "Units.h"
+#include "mozilla/ToString.h"
 
 #include <limits>
 #include <algorithm>
@@ -2170,6 +2171,34 @@ public:
    */
   static bool WantSubAPZC();
 
+  /**
+   * Log a key/value pair for APZ testing during a paint.
+   * @param aPresShell The pres shell that identifies where to log to. The data
+   *                   will be written to the APZTestData associated with the
+   *                   pres shell's layer manager.
+   * @param aScrollId Identifies the scroll frame to which the data pertains.
+   * @param aKey The key under which to log the data.
+   * @param aValue The value of the data to be logged.
+   */
+  static void LogTestDataForPaint(nsIPresShell* aPresShell,
+                                  ViewID aScrollId,
+                                  const std::string& aKey,
+                                  const std::string& aValue);
+
+  /**
+   * A convenience overload of LogTestDataForPaint() that accepts any type
+   * as the value, and passes it through mozilla::ToString() to obtain a string
+   * value. The type passed must support streaming to an std::ostream.
+   */
+  template <typename Value>
+  static void LogTestDataForPaint(nsIPresShell* aPresShell,
+                                  ViewID aScrollId,
+                                  const std::string& aKey,
+                                  const Value& aValue) {
+    LogTestDataForPaint(aPresShell, aScrollId, aKey,
+        mozilla::ToString(aValue));
+  }
+
  /**
    * Get the display port for |aScrollFrame|'s content. If |aScrollFrame|
    * WantsAsyncScroll() and we don't have a scrollable displayport yet (as