Attach a WebLayer to a frame element for out-of-process iframes.

Source/core/frame/Frame.h

Index: Source/core/frame/Frame.h
diff --git a/Source/core/frame/Frame.h b/Source/core/frame/Frame.h
index 6c38bceb8f3e6555c648ff2c2218c8e504961ac8..8148fdd88fd5b082abb80a3b211251e43332a690 100644
--- a/Source/core/frame/Frame.h
+++ b/Source/core/frame/Frame.h
@@ -37,6 +37,10 @@
 #include "wtf/Forward.h"
 #include "wtf/RefCounted.h"
 
+namespace blink {
+class WebLayer;
+}
+
 namespace WebCore {
 
     class AnimationController;
@@ -152,6 +156,9 @@ namespace WebCore {
 
         int64_t frameID() const { return m_frameInit->frameID(); }
 
+        void setPlatformLayer(blink::WebLayer* platformLayer) { m_platformLayer = platformLayer; }

[eseidel, 2013/12/11 18:50:01]

I would give this a less generic name.  setRemotePlatformLayer?

I would also ideally compile-time guard this and only have it on for OOPI
enabled builds.  We don't generally do large experiments like this on trunk
(e.g. oilpan).  OOPI's design doesn't seem solidified and we're still
experimenting here.

[ncarter (slow), 2013/12/11 21:28:11]

Is the oilpan comparison apt? I think our design is fairly solidified, but as
with all software development, the act of reducing the design to code will
involve some process of discovery and experimentation.

A compile-time guard puts a substantial burden on development: you now need a
custom builder for any kind of test automation, which in practice may mean that
we simply won't have tests running on trybots or builders until we are ready to
drop the #define. It also adds significant friction to switching a local build
into the OOPIF mode, which may inhibit our ability to successfully convince
domain experts to jump in and offer a hand in development.

In my opinion, protecting the codepath with a runtime flag would be a better
choice, provided of course that this is acceptable from a regression-risk
perspective.

+        blink::WebLayer* platformLayer() const { return m_platformLayer; }
+
     // ======== All public functions below this point are candidates to move out of Frame into another class. ========
 
         bool inScope(TreeScope*) const;
@@ -236,6 +243,9 @@ namespace WebCore {
 #endif
 
         bool m_inViewSourceMode;
+
+        // This layer is for frames whose contents are being rendered in a separate process.

[eseidel, 2013/12/11 18:50:01]

You could just convey that in the member name.

[kenrb, 2013/12/11 22:44:56]

Done.

+        blink::WebLayer* m_platformLayer;
     };
 
     inline void Frame::init()