Split ImageResourceClient into ResourceClient and ImageResourceObserver [1/2]

We are planning to move ResourceClient to on-heap, but LayoutObject (an
ImageResourceClient subclass) is hard to move to on-heap.

This series of CLs splits ImageResourceClient into
- ResourceClient (notified via Resource, to be moved to Oilpan heap) and
- ImageResourceObserver (notified via ImageObserver, to remain non-heap)
and makes LayoutObject to be ImageResourceObserver but not ResourceClient.

This is the [1/2] CL that
- Splits ImageResourceClient into ResourceClient and ImageResourceObserver,
- Makes LayoutObject and all of its subclasses (except for LayoutImage and its
  subclasses) to be ImageResourceObserver but not ResourceClient.

LayoutImage will be made non-ResourceClient by the [2/2] CL:
https://codereview.chromium.org/1728313003/.

Original CL: https://codereview.chromium.org/1697713002/ by Nate Chapin.

In addition to Nate's original CL (Patch Set 1), this CL:
- Fixes layout test (Patch Set 2).
- Reuses ResourceClientWalker to iterate ImageResourceObserver (Patch Set 3).
- Handles ResourceClient and ImageResourceObserver more similarly (Patch Set 4).
- Renames methods to reflect whether they are for both ResourceClient and
  ImageResourceObserver (Patch Set 6).

BUG=587663

Review URL: https://codereview.chromium.org/1706083002

Cr-Commit-Position: refs/heads/master@{#383425}

1 files changed, 3 insertions, 1 deletions

diff --git a/third_party/WebKit/Source/core/layout/LayoutImage.h b/third_party/WebKit/Source/core/layout/LayoutImage.h
index b162c7e..c81ed4e 100644
--- a/third_party/WebKit/Source/core/layout/LayoutImage.h
+++ b/third_party/WebKit/Source/core/layout/LayoutImage.h
@@ -26,6 +26,7 @@
 #define LayoutImage_h
 
 #include "core/CoreExport.h"
+#include "core/fetch/ResourceClient.h"
 #include "core/layout/LayoutImageResource.h"
 #include "core/layout/LayoutReplaced.h"
 
@@ -43,7 +44,7 @@ class HTMLMapElement;
 //
 // The class is image type agnostic as it only manipulates decoded images.
 // See LayoutImageResource that holds this image.
-class CORE_EXPORT LayoutImage : public LayoutReplaced {
+class CORE_EXPORT LayoutImage : public LayoutReplaced, public ResourceClient {
 public:
     // These are the paddings to use when displaying either alt text or an image.
     static const unsigned short paddingWidth = 4;
@@ -77,6 +78,7 @@ public:
     }
 
     const char* name() const override { return "LayoutImage"; }
+    String debugName() const final { return LayoutObject::debugName(); }
 
 protected:
     bool needsPreferredWidthsRecalculation() const final;