[reland] SegmentedString::push() should always push a char in front

Source/platform/text/SegmentedStringTest.cpp

Index: Source/platform/text/SegmentedStringTest.cpp
diff --git a/Source/platform/text/SegmentedStringTest.cpp b/Source/platform/text/SegmentedStringTest.cpp
index b033bd5f7170c55ae6b6110e6f584c7558f5e8c1..5aec779fbef16d4e0d8e8e5311053eefb0524bfa 100644
--- a/Source/platform/text/SegmentedStringTest.cpp
+++ b/Source/platform/text/SegmentedStringTest.cpp
@@ -47,20 +47,18 @@ TEST(SegmentedStringTest, CurrentChar)
         EXPECT_EQ('c', copied.currentChar());
         EXPECT_EQ('c', assigned.currentChar());
     }
-    original.push('a');
+    original.push('b');
     {
         SegmentedString copied(original);
         SegmentedString assigned;
         assigned = original;
-        EXPECT_EQ("acde", original.toString());
-        EXPECT_EQ('a', original.currentChar());
-        EXPECT_EQ('a', copied.currentChar());
-        EXPECT_EQ('a', assigned.currentChar());
+        EXPECT_EQ("bcde", original.toString());
+        EXPECT_EQ('b', original.currentChar());
+        EXPECT_EQ('b', copied.currentChar());
+        EXPECT_EQ('b', assigned.currentChar());
     }
-    original.push('b');
+    original.push('a');
     {
-        // Two consecutive push means to push the second char *after* the
-        // first char in SegmentedString.
         SegmentedString copied(original);
         SegmentedString assigned;
         assigned = original;