Heap profiler: implement diffing of snapshots.

src/checks.h

Index: src/checks.h
diff --git a/src/checks.h b/src/checks.h
index 13374d86dda4994474598dec85a232b70fdb483d..05db5742222162ae6c1b0e668c1a4b7c78bc5b64 100644
--- a/src/checks.h
+++ b/src/checks.h
@@ -103,6 +103,28 @@ static inline void CheckEqualsHelper(const char* file, int line,
 }
 
 
+// Helper function used by the CHECK_EQ function when given uint64_t
+// arguments.  Should not be called directly.
+static inline void CheckEqualsHelper(const char* file, int line,
+                                     const char* expected_source,
+                                     uint64_t expected,
+                                     const char* value_source,
+                                     uint64_t value) {
+  if (expected != value) {
+    // Print uint64_t values in hex, as two int32s,
+    // to avoid platform-dependencies.
+    V8_Fatal(file, line,
+             "CHECK_EQ(%s, %s) failed\n#"
+             "   Expected: 0x%08x%08x\n#   Found: 0x%08x%08x",
+             expected_source, value_source,
+             static_cast<uint32_t>(expected >> 32),
+             static_cast<uint32_t>(expected),
+             static_cast<uint32_t>(value >> 32),
+             static_cast<uint32_t>(value));
+  }
+}
+
+
 // Helper function used by the CHECK_NE function when given int
 // arguments.  Should not be called directly.
 static inline void CheckNonEqualsHelper(const char* file,