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..9252537a4ebd49852dc2926b1c55e37de2a90175 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"
@@ -145,6 +146,10 @@
 
 namespace blink {
 
+// A4 Portrait dimensions in pixels
+const int kA4PortraitPageWidth = 595;
+const int kA4PortraitPageHeight = 842;
+
 using namespace HTMLNames;
 
 // The maximum number of updateWidgets iterations that should be done before
@@ -234,6 +239,7 @@ 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 +2892,36 @@ 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();
+  }
+}
+
+void FrameView::setupPrintContext() {
+  if (!m_frame->document()->printing()) {

[mstensho (USE GERRIT), 2017/02/08 14:32:29]

Could consider an early return here; i.e.:

  if (m_frame->document()->printing())
    return;
  // The rest of the code goes here.

That at least used to be preferred Blink style.

[gozzard, 2017/02/09 04:17:25]

Done.

+    if (!m_printContext)
+      m_printContext = new PrintContext(m_frame);
+    if (m_frame->settings())
+      m_frame->settings()->setShouldPrintBackgrounds(true);
+    FloatRect pageRect(0, 0, kA4PortraitPageWidth, kA4PortraitPageHeight);
+    m_printContext->begin(pageRect.width(), pageRect.height());
+    float height;
+    m_printContext->computePageRects(pageRect, 0, 0, 1.0, height);
+    dispatchEventsForPrintingOnAllFrames();

[pdr., 2017/02/08 06:34:08]

Could you use forAllNonThrottledFrameViews for this?

I.e.,
forAllNonThrottledFrameViews([](FrameView& frameView) {
  frameView.frame().document()->dispatchEventsForPrinting();
});

[gozzard, 2017/02/09 04:17:25]

dispatchEventsForPrinting() ultimately informs some listeners of the media query
change and shuffles any print-related events down to our children. This will not
be run frequently, and seems inadvisable to skip, so we would want to apply this
for throttled FrameViews also. If there existed a forAllFrameViews() variant of
this helper function that may be appropriate, but it would be a simple thin
wrapper around this loop anyway, so I am not inclined to implement such a
helper.

+  }

[pdr., 2017/02/08 06:34:08]

I think this approach can fail to dispatch print events if a subframe has not
yet loaded. For example, if we have a page with an iframe'd ad and we hit this
code before the ad loads, will we fail to ever dispatch the printing event to
the ad? If so, can you add a TODO(gozzard): comment mentioning this?

[gozzard, 2017/02/09 04:17:25]

This appears to be the case. However, I believe this is expected behaviour. The
only endpoints I am aware of for the dispatchEvent() system are javascript
listeners. If the javascript has not yet loaded/executed, it should handle
checking the current state of the page itself, if it is interested. I believe it
is by design that this only notifies existing, registered listeners. Using
printing as an example: It simply triggers any registered MediaQueryList
listeners. The javascript must query for the current MediaQueryList state before
it can even register a listener. If there are any internal events, then they
should follow suit and check the current state on initialization.

+}
+
+void FrameView::clearPrintContext() {
+  if (m_printContext) {

[mstensho (USE GERRIT), 2017/02/08 14:32:29]

Might even consider an early return on !m_printContext here.

[gozzard, 2017/02/09 04:17:26]

Done.

+    m_printContext->end();
+    m_printContext.clear();
+  }
+}
+
 // TODO(leviw): We don't assert lifecycle information from documents in child
 // PluginViews.
 void FrameView::updateLifecyclePhasesInternal(
@@ -2918,6 +2954,12 @@ void FrameView::updateLifecyclePhasesInternal(
     return;
   }
 
+  if (RuntimeEnabledFeatures::printBrowserEnabled()) {
+    setupPrintContext();
+  } else {
+    clearPrintContext();
+  }

[mstensho (USE GERRIT), 2017/02/08 14:32:29]

No need for the curly braces.

[gozzard, 2017/02/09 04:17:25]

Done.

+
   updateStyleAndLayoutIfNeededRecursive();
   DCHECK(lifecycle().state() >= DocumentLifecycle::LayoutClean);
 
@@ -2990,7 +3032,8 @@ 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 +3125,8 @@ void FrameView::paintTree() {
   if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
     if (layoutView()->layer()->needsRepaint()) {
       GraphicsContext graphicsContext(*m_paintController);
+      if (RuntimeEnabledFeatures::printBrowserEnabled())
+        graphicsContext.setPrinting(true);
       paint(graphicsContext, CullRect(LayoutRect::infiniteIntRect()));
       m_paintController->commitNewDisplayItems(LayoutSize());
       notifyPaint(*m_paintController);