Simplify CompositingReasonFinder::requiresCompositingForFrame

This CL removes an optimization whereby 0x0 iframes wouldn't get a composited
layer even if they would otherwise have been composited. This optimization was
causing a bunch of awkwardness because it introduced a dependency on layout
information in the CompositingReasonFinder, which caused the reason finder to
need to set a dirty bit in the RenderLayerCompositor.

This CL also prepares us to remove requiresCompositingForFrame into a
RenderPart-specific override of additionalCompositingReasons (after
https://codereview.chromium.org/197533013/ lands).

This CL also changes RenderLayerCompositor::enableCompositingMode to notify
iframes when the root layer is destroyed as well instead of relying upon the
CompositingReasonFinder to write the dirty bit.

R=vollick@chromium.org

Review URL: https://codereview.chromium.org/206243003

git-svn-id: svn://svn.chromium.org/blink/trunk@169679 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/LayoutTests/compositing/iframes/iframe-size-to-zero-expected.txt

 
-PASS: had layers, and now do not
+PASS: Had layers before and after

third_party/WebKit/LayoutTests/compositing/iframes/iframe-size-to-zero.html

@@ -46,10 +46,10 @@
             if (window.testRunner) {
                 var haveLayers = window.internals.layerTreeAsText(document) != "";
                 var result;
-                if (hadLayers && !haveLayers)
-                  result = "PASS: had layers, and now do not";
+                if (hadLayers && haveLayers)
+                  result = "PASS: Had layers before and after";
                 else
-                  result = "FAIL: layers should have gone. hadLayers = " + hadLayers + ", haveLayers = " + haveLayers;
+                  result = "FAIL: Layers should have stayed. hadLayers = " + hadLayers + ", haveLayers = " + haveLayers;
                 document.getElementById('result').innerHTML = result;
                 testRunner.notifyDone();
             }

third_party/WebKit/Source/core/rendering/compositing/CompositingReasonFinder.cpp

@@ -74,7 +74,7 @@ CompositingReasons CompositingReasonFinder::directReasons(const RenderLayer* lay
         directReasons |= CompositingReasonCanvas;
     else if (requiresCompositingForPlugin(renderer, needToRecomputeCompositingRequirements))
         directReasons |= CompositingReasonPlugin;
-    else if (requiresCompositingForFrame(renderer, needToRecomputeCompositingRequirements))
+    else if (requiresCompositingForFrame(renderer))
         directReasons |= CompositingReasonIFrame;
 
     if (requiresCompositingForBackfaceVisibilityHidden(renderer))
@@ -183,33 +183,9 @@ bool CompositingReasonFinder::requiresCompositingForPlugin(RenderObject* rendere
     return contentBox.height() * contentBox.width() > 1;
 }
 
-bool CompositingReasonFinder::requiresCompositingForFrame(RenderObject* renderer, bool* needToRecomputeCompositingRequirements) const
+bool CompositingReasonFinder::requiresCompositingForFrame(RenderObject* renderer) const
 {
-    if (!renderer->isRenderPart())
-        return false;
-
-    RenderPart* frameRenderer = toRenderPart(renderer);
-
-    if (!frameRenderer->requiresAcceleratedCompositing())
-        return false;
-
-    if (frameRenderer->node() && frameRenderer->node()->isFrameOwnerElement() && toHTMLFrameOwnerElement(frameRenderer->node())->contentFrame() && toHTMLFrameOwnerElement(frameRenderer->node())->contentFrame()->remotePlatformLayer())
-        return true;
-
-    // FIXME: this seems bogus. If we don't know the layout position/size of the frame yet, wouldn't that be handled elsehwere?
-    *needToRecomputeCompositingRequirements = true;
-
-    RenderLayerCompositor* innerCompositor = RenderLayerCompositor::frameContentsCompositor(frameRenderer);
-    if (!innerCompositor)
-        return false;
-
-    // If we can't reliably know the size of the iframe yet, don't change compositing state.
-    if (renderer->needsLayout())
-        return frameRenderer->hasLayer() && frameRenderer->layer()->hasCompositedLayerMapping();
-
-    // Don't go into compositing mode if height or width are zero.
-    IntRect contentBox = pixelSnappedIntRect(frameRenderer->contentBoxRect());
-    return contentBox.height() * contentBox.width() > 0;
+    return renderer->isRenderPart() && toRenderPart(renderer)->requiresAcceleratedCompositing();
 }
 
 bool CompositingReasonFinder::requiresCompositingForBackfaceVisibilityHidden(RenderObject* renderer) const

third_party/WebKit/Source/core/rendering/compositing/CompositingReasonFinder.h

@@ -41,7 +41,7 @@ private:
     bool requiresCompositingForVideo(RenderObject*) const;
     bool requiresCompositingForCanvas(RenderObject*) const;
     bool requiresCompositingForPlugin(RenderObject*, bool* needToRecomputeCompositingRequirements) const;
-    bool requiresCompositingForFrame(RenderObject*, bool* needToRecomputeCompositingRequirements) const;
+    bool requiresCompositingForFrame(RenderObject*) const;
     bool requiresCompositingForBackfaceVisibilityHidden(RenderObject*) const;
     bool requiresCompositingForFilters(RenderObject*) const;
     bool requiresCompositingForOverflowScrollingParent(const RenderLayer*) const;

third_party/WebKit/Source/core/rendering/compositing/RenderLayerCompositor.cpp

@@ -219,17 +219,19 @@ RenderLayerCompositor::~RenderLayerCompositor()
     ASSERT(m_rootLayerAttachment == RootLayerUnattached);
 }
 
-void RenderLayerCompositor::enableCompositingMode(bool enable /* = true */)
+void RenderLayerCompositor::enableCompositingMode(bool enable)
 {
-    if (enable != m_compositing) {
-        m_compositing = enable;
+    if (enable == m_compositing)
+        return;
 
-        if (m_compositing) {
-            ensureRootLayer();
-            notifyIFramesOfCompositingChange();
-        } else
-            destroyRootLayer();
-    }
+    m_compositing = enable;
+
+    if (m_compositing)
+        ensureRootLayer();
+    else
+        destroyRootLayer();
+
+    notifyIFramesOfCompositingChange();
 }
 
 void RenderLayerCompositor::cacheAcceleratedCompositingFlags()