Revert of PaintChunk::id

third_party/WebKit/Source/platform/graphics/paint/PaintChunk.h

Index: third_party/WebKit/Source/platform/graphics/paint/PaintChunk.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintChunk.h b/third_party/WebKit/Source/platform/graphics/paint/PaintChunk.h
index a23c84f530d36573f7cb431035f878e733719a38..bafb8298ecdc2ba775afed614f996c1d485bfab7 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintChunk.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintChunk.h
@@ -6,10 +6,8 @@
 #define PaintChunk_h
 
 #include "platform/geometry/FloatRect.h"
-#include "platform/graphics/paint/DisplayItem.h"
 #include "platform/graphics/paint/PaintChunkProperties.h"
 #include "wtf/Allocator.h"
-#include "wtf/Optional.h"
 #include <iosfwd>
 
 namespace blink {
@@ -23,35 +21,13 @@
 struct PaintChunk {
     DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
     PaintChunk() : beginIndex(0), endIndex(0), knownToBeOpaque(false) { }
-    PaintChunk(unsigned begin, unsigned end, const DisplayItem::Id* chunkId, const PaintChunkProperties& props)
-        : beginIndex(begin), endIndex(end), properties(props), knownToBeOpaque(false)
-    {
-        if (chunkId)
-            id.emplace(*chunkId);
-    }
+    PaintChunk(unsigned begin, unsigned end, const PaintChunkProperties& props)
+        : beginIndex(begin), endIndex(end), properties(props), knownToBeOpaque(false) { }
 
     unsigned size() const
     {
         ASSERT(endIndex >= beginIndex);
         return endIndex - beginIndex;
-    }
-
-    // Check if a new PaintChunk (this) created in the latest paint matches an old
-    // PaintChunk created in the previous paint.
-    bool matches(const PaintChunk& old) const
-    {
-        // A PaintChunk without an id doesn't match any other PaintChunks.
-        if (!id || !old.id)
-            return false;
-        if (*id != *old.id)
-            return false;
-#if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
-        CHECK(id->client.isAlive());
-#endif
-        // A chunk whose client is just created should not match any cached chunk,
-        // even if it's id equals the old chunk's id (which may happen if this chunk's
-        // client is just created at the same address of the old chunk's deleted client).
-        return !id->client.isJustCreated();
     }
 
     // Index of the first drawing in this chunk.
@@ -60,15 +36,6 @@
     // Index of the first drawing not in this chunk, so that there are
     // |endIndex - beginIndex| drawings in the chunk.
     unsigned endIndex;
-
-    // Identifier of this chunk. If it has a value, it should be unique.
-    // It's used to match a new chunk to a cached old chunk to track changes of chunk
-    // contents, so the id should be stable across document cycles.
-    // If the contents of the chunk can't be cached (e.g. it's created when PaintController
-    // is skipping cache, normally because display items can't be uniquely identified),
-    // id is nullopt so that the chunk won't match any other chunk.
-    using Id = DisplayItem::Id;
-    Optional<Id> id;
 
     // The paint properties which apply to this chunk.
     PaintChunkProperties properties;
@@ -84,7 +51,6 @@
 {
     return a.beginIndex == b.beginIndex
         && a.endIndex == b.endIndex
-        && a.id == b.id
         && a.properties == b.properties
         && a.bounds == b.bounds
         && a.knownToBeOpaque == b.knownToBeOpaque;