Add base::PickleIterator::ReachedEnd()

This can be useful if a bit of data serialized at the end is optional;
instead of having to encode an explicit boolean flag, the deserializer
can simply consult ReachedEnd().

Bug: 1055911
Change-Id: Id92bfa5ffbdd0c309367417ed12444eff2d94cb4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2091715
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747909}

base/pickle.h

@@ -75,6 +75,8 @@ class BASE_EXPORT PickleIterator {
     return !!GetReadPointerAndAdvance(num_bytes);
   }
 
+  bool ReachedEnd() const { return read_index_ == end_index_; }
+
  private:
   // Read Type from Pickle.
   template <typename Type>

base/pickle_unittest.cc

@@ -570,4 +570,30 @@ TEST(PickleTest, ClaimBytes) {
   EXPECT_EQ(42, out_value);
 }
 
+TEST(PickleTest, ReachedEnd) {
+  Pickle pickle;
+  pickle.WriteInt(1);
+  pickle.WriteInt(2);
+  pickle.WriteInt(3);
+
+  PickleIterator iter(pickle);
+  int out;
+
+  EXPECT_FALSE(iter.ReachedEnd());
+  EXPECT_TRUE(iter.ReadInt(&out));
+  EXPECT_EQ(1, out);
+
+  EXPECT_FALSE(iter.ReachedEnd());
+  EXPECT_TRUE(iter.ReadInt(&out));
+  EXPECT_EQ(2, out);
+
+  EXPECT_FALSE(iter.ReachedEnd());
+  EXPECT_TRUE(iter.ReadInt(&out));
+  EXPECT_EQ(3, out);
+
+  EXPECT_TRUE(iter.ReachedEnd());
+  EXPECT_FALSE(iter.ReadInt(&out));
+  EXPECT_TRUE(iter.ReachedEnd());
+}
+
 }  // namespace base