VectorComparer should check null.

We use VectorComparer to compare WTF::Vector<T>.
If T is not primitive type, we use std::equal to compare.
By the way, we use the WTF::VectorBufferBase class for a base class of Vector.  VectorBufferBase doesn't alloc a array if we init it without a size argument.
As a conclusion, we pass NULL object to std::equal when we compare Vectors with the default constructor.
It is asserted especially on a Windows debug build.

BUG=

Review URL: https://codereview.chromium.org/332113002

git-svn-id: svn://svn.chromium.org/blink/trunk@176189 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/wtf/Vector.h

@@ -224,7 +224,9 @@ static const size_t kInitialVectorSize = WTF_VECTOR_INITIAL_SIZE;
     {
         static bool compare(const T* a, const T* b, size_t size)
         {
-            return std::equal(a, a + size, b);
+            if (LIKELY(a && b))
+                return std::equal(a, a + size, b);
+            return !a && !b;
         }
     };
 

third_party/WebKit/Source/wtf/VectorTest.cpp

@@ -28,6 +28,7 @@
 #include "wtf/HashSet.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
+#include "wtf/text/WTFString.h"
 #include "wtf/Vector.h"
 #include <gtest/gtest.h>
 
@@ -283,4 +284,22 @@ TEST(VectorTest, SwapWithInlineCapacity)
     vectorB.swap(vectorA);
 }
 
+class Comparable {
+};
+bool operator==(const Comparable& a, const Comparable& b) { return true; }
+
+template<typename T> void compare()
+{
+    EXPECT_TRUE(Vector<T>() == Vector<T>());
+    EXPECT_FALSE(Vector<T>(1) == Vector<T>(0));
+    EXPECT_FALSE(Vector<T>() == Vector<T>(1));
+    EXPECT_TRUE(Vector<T>(1) == Vector<T>(1));
+}
+
+TEST(VectorTest, Compare)
+{
+    compare<int>();
+    compare<Comparable>();
+    compare<WTF::String>();
+}
 } // namespace