Implements PrintBrowser mode.

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index 93a42bb40dca6076bc944a1ef652c21933171a5a..e22aff294f003c1e7b72fb7137f19b354251c9f7 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -90,6 +90,7 @@
 #include "core/page/FocusController.h"
 #include "core/page/FrameTree.h"
 #include "core/page/Page.h"
+#include "core/page/PrintContext.h"
 #include "core/page/scrolling/RootScrollerUtil.h"
 #include "core/page/scrolling/ScrollingCoordinator.h"
 #include "core/page/scrolling/TopDocumentRootScrollerController.h"
@@ -234,6 +235,7 @@ DEFINE_TRACE(FrameView) {
   visitor->trace(m_scrollAnchor);
   visitor->trace(m_anchoringAdjustmentQueue);
   visitor->trace(m_scrollbarManager);
+  visitor->trace(m_printContext);
   Widget::trace(visitor);
   ScrollableArea::trace(visitor);
 }
@@ -2886,6 +2888,15 @@ void FrameView::notifyResizeObservers() {
   DCHECK(!layoutView()->needsLayout());
 }
 
+void FrameView::dispatchEventsForPrintingOnAllFrames() {
+  DCHECK(m_frame->isMainFrame());
+  for (Frame* currentFrame = m_frame; currentFrame;
+       currentFrame = currentFrame->tree().traverseNext(m_frame)) {
+    if (currentFrame->isLocalFrame())
+      toLocalFrame(currentFrame)->document()->dispatchEventsForPrinting();
+  }
+}
+
 // TODO(leviw): We don't assert lifecycle information from documents in child
 // PluginViews.
 void FrameView::updateLifecyclePhasesInternal(
@@ -2918,6 +2929,24 @@ void FrameView::updateLifecyclePhasesInternal(
     return;
   }
 
+  if (RuntimeEnabledFeatures::printBrowserEnabled()) {
+    if (!m_frame->document()->printing()) {

[pdr., 2017/02/08 04:28:05]

Can you split this logic out into a helper? I think that will help keep
updateLifecyclePhasesInternal simple.

[gozzard, 2017/02/08 05:40:20]

Done.

+      if (!m_printContext)
+        m_printContext = new PrintContext(m_frame);
+      if (m_frame->settings())
+        m_frame->settings()->setShouldPrintBackgrounds(true);
+      int pageWidth = 595, pageHeight = 842;  // A4 Portrait

[pdr., 2017/02/08 04:28:05]

Nit: can you break these into constants?
Maybe "const int kA4PortraitPageWidth = 595;"

[gozzard, 2017/02/08 05:40:20]

Done.

+      FloatRect pageRect(0, 0, pageWidth, pageHeight);
+      m_printContext->begin(pageRect.width(), pageRect.height());
+      float height;

[pdr., 2017/02/08 04:28:05]

Do we need to do this print context and page rect computations and event
dispatching on every call to updateLifecyclePhasesInternal?

[gozzard, 2017/02/08 05:40:20]

m_printContext->begin() indirectly sets m_frame->document()->printing() to be
true. As such this setup code will only runs as necessary.

+      m_printContext->computePageRects(pageRect, 0, 0, 1.0, height);
+      dispatchEventsForPrintingOnAllFrames();
+    }
+  } else if (m_printContext) {
+    m_printContext->end();
+    m_printContext.clear();
+  }
+
   updateStyleAndLayoutIfNeededRecursive();
   DCHECK(lifecycle().state() >= DocumentLifecycle::LayoutClean);
 
@@ -2990,7 +3019,8 @@ void FrameView::updateLifecyclePhasesInternal(
       DocumentAnimations::updateAnimations(layoutView()->document());
 
     if (targetState == DocumentLifecycle::PaintClean) {
-      if (!m_frame->document()->printing())
+      if (!m_frame->document()->printing() ||
+          RuntimeEnabledFeatures::printBrowserEnabled())
         paintTree();
 
       if (RuntimeEnabledFeatures::slimmingPaintV2Enabled())
@@ -3082,6 +3112,8 @@ void FrameView::paintTree() {
   if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
     if (layoutView()->layer()->needsRepaint()) {
       GraphicsContext graphicsContext(*m_paintController);
+      if (RuntimeEnabledFeatures::printBrowserEnabled())

[pdr., 2017/02/08 04:28:05]

WDYT about implementing this for both spv2 (as you've done here) and the spv1
codepaths? I think it should be pretty easy to do and will make sure this
feature isn't tied to spv2's timeline.

If you do this, please add a layouttest that covers both codepaths. The virtual
test infrastructure lets you write tests that run with a flag. It's a little
confusing so please ask if you need help with this.

[gozzard, 2017/02/08 05:40:20]

I had a look into this and found that it would require significantly more
boilerplate to implement support for SPV1. Therefore we made the design decision
to (at least initially) only support SPV2. This may no longer be the case after
changing to RuntimeEnabledFeatures::printBrowserEnabled(). I will look into it,
but I think this is best done as a separate CL, especially as I probably don't
have the time left in my internship to do this.
I just finished setting this up with a virtual test environment and an example
test anyway, actually.

+        graphicsContext.setPrinting(true);
       paint(graphicsContext, CullRect(LayoutRect::infiniteIntRect()));
       m_paintController->commitNewDisplayItems(LayoutSize());
       notifyPaint(*m_paintController);