Disable copy and assignment for DisplayItemClient

The copy constructor breaks DisplayItemClient aliveness checking.
We could fix the copy constructor but it looks better not to support
the copy constructor.
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2611923002
Cr-Commit-Position: refs/heads/master@{#441432}

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

@@ -45,6 +45,7 @@ class PLATFORM_EXPORT DisplayItemClient {
   static void endShouldKeepAliveAllClients(const void* owner);
   static void endShouldKeepAliveAllClients();
 #else
+  DisplayItemClient() {}
   virtual ~DisplayItemClient() {}
 #endif
 
@@ -171,6 +172,8 @@ class PLATFORM_EXPORT DisplayItemClient {
 
   mutable CacheGenerationOrInvalidationReason
       m_cacheGenerationOrInvalidationReason;
+
+  DISALLOW_COPY_AND_ASSIGN(DisplayItemClient);
 };
 
 inline bool operator==(const DisplayItemClient& client1,