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

- Bug 1248822 - In LayerManagerComposite::UpdateAndRender(), call PostProcessLayers() before LayerTreeInvalidation. r=mattwoodrow (503f81f51f)
- Bug 1259541 - Reduce clearing backbuffer in nsBaseWidget::CreateBackBufferDrawTarget() r=mattwoodrow (4f8cf8ab04)
- Bug 1174461 - [e10s] Return a cached result from SendGetNativePluginPort (r=jimm) a=kwierso (fff65b95ac)
- Bug 1263200 - Reset the APZ pointer in the base widget to null if the compositor creation fails. r=mstange (109d4a16a8)
- Bug 1264161 - Ensure we null out APZ pointers to the widget when it gets destroyed. r=botond (fdb516451e)
- Bug 1260018 - Route drag events to APZ, so it can accurately detect the end of a drag. r=kats (acd2b4a051)
- Remove drawWidgetAsOnScreen. (bug 1264393, r=mattwoodrow, webidl r=khuey) (b0ce23eacc)
- Bug 1254151 - use B8G8R8X8 for 24 bit depth visuals in nsShmImage with Cairo. r=jrmuizel (070ef9495d)
- Bug 1218955 - Remove nsIMEPicker, r=jchen (83adb6c582)
- Bug 1255655 - Const-ify keysymtab. r=karlt. (d9544cbf0c)
- Bug 1165048 - Music playback is getting stopped and is not resumed when modem is restarted. r=mwu (d3f99f8542)
- Bug 1264183. Remove unused argument to nsView::InvalidateHierarchy. r=mats (218ce04623)
- Bug 1210617 - [e10s] Implement PrivateBrowsingChannel for ExternalHelperAppParent. r=jduell (36e6ab7635)
- Bug 1258087 - Fix -Wunreachable-code warning in StartupCache.cpp on macosx64-mulet. r=froydnj (5f88df6993)
- Bug 1329798 - Include sys/sysmacros.h for major(), minor() on Linux. r=glandium, a=jcristau (a5c4073eb2)
- guard for non-linux system again or mac & FreeBSD fail to compile (6b5d2856b6)

gfx/layers/basic/BasicCompositor.cpp

@@ -162,7 +162,7 @@ BasicCompositor::CreateRenderTargetFromSource(const IntRect &aRect,
 }
 
 already_AddRefed<CompositingRenderTarget>
-BasicCompositor::CreateRenderTargetForWindow(const LayoutDeviceIntRect& aRect, SurfaceInitMode aInit, BufferMode aBufferMode)
+BasicCompositor::CreateRenderTargetForWindow(const LayoutDeviceIntRect& aRect, const LayoutDeviceIntRect& aClearRect, BufferMode aBufferMode)
 {
   MOZ_ASSERT(mDrawTarget);
   MOZ_ASSERT(aRect.width != 0 && aRect.height != 0, "Trying to create a render target of invalid size");
@@ -175,7 +175,7 @@ BasicCompositor::CreateRenderTargetForWindow(const LayoutDeviceIntRect& aRect, S
   IntRect rect = aRect.ToUnknownRect();
 
   if (aBufferMode != BufferMode::BUFFER_NONE) {
-    RefPtr<DrawTarget> target = mWidget->CreateBackBufferDrawTarget(mDrawTarget, aRect, aInit == INIT_MODE_CLEAR);
+    RefPtr<DrawTarget> target = mWidget->CreateBackBufferDrawTarget(mDrawTarget, aRect, aClearRect);
     if (!target) {
       return nullptr;
     }
@@ -187,8 +187,9 @@ BasicCompositor::CreateRenderTargetForWindow(const LayoutDeviceIntRect& aRect, S
       windowRect.ExpandToEnclose(IntPoint(0, 0));
     }
     rt = new BasicCompositingRenderTarget(mDrawTarget, windowRect);
-    if (aInit == INIT_MODE_CLEAR) {
-      mDrawTarget->ClearRect(Rect(rect - rt->GetOrigin()));
+    if (!aClearRect.IsEmpty()) {
+      IntRect clearRect = aRect.ToUnknownRect();
+      mDrawTarget->ClearRect(Rect(clearRect - rt->GetOrigin()));
     }
   }
 
@@ -476,7 +477,7 @@ void
 BasicCompositor::BeginFrame(const nsIntRegion& aInvalidRegion,
                             const gfx::Rect *aClipRectIn,
                             const gfx::Rect& aRenderBounds,
-                            bool aOpaque,
+                            const nsIntRegion& aOpaqueRegion,
                             gfx::Rect *aClipRectOut /* = nullptr */,
                             gfx::Rect *aRenderBoundsOut /* = nullptr */)
 {
@@ -524,11 +525,20 @@ BasicCompositor::BeginFrame(const nsIntRegion& aInvalidRegion,
     return;
   }
 
+  LayoutDeviceIntRect clearRect;
+  if (!aOpaqueRegion.IsEmpty()) {
+    LayoutDeviceIntRegion clearRegion = mInvalidRegion;
+    clearRegion.SubOut(LayoutDeviceIntRegion::FromUnknownRegion(aOpaqueRegion));
+    clearRect = clearRegion.GetBounds();
+  } else {
+    clearRect = mInvalidRect;
+  }
+
   // Setup an intermediate render target to buffer all compositing. We will
   // copy this into mDrawTarget (the widget), and/or mTarget in EndFrame()
   RefPtr<CompositingRenderTarget> target =
     CreateRenderTargetForWindow(mInvalidRect,
-                                aOpaque ? INIT_MODE_NONE : INIT_MODE_CLEAR,
+                                clearRect,
                                 bufferMode);
   if (!target) {
     if (!mTarget) {