Revert "Reland [parser] Refactor streaming scanner streams."

This reverts commit 7fa071a4.

Reason for revert: https://bugs.chromium.org/p/chromium/issues/detail?id=729482

Original change's description:
> Reland [parser] Refactor streaming scanner streams.
> 
> Unify, simplify logic, reduce UTF8 specific handling.
> 
> Intend of this is also to have stream views.
> Stream views can be used concurrently by multiple threads, but
> only one thread may fetch new data from the underlying source.
> This together with unified stream view creation is intended to be
> used for parse tasks.
> 
> BUG=v8:6093
> 
> Change-Id: I3bce48185fa2c986d16619a9a8ece3ff4c4f5e60
> Reviewed-on: https://chromium-review.googlesource.com/509489
> Reviewed-by: Daniel Vogelheim <vogelheim@chromium.org>
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Commit-Queue: Wiktor Garbacz <wiktorg@google.com>
> Cr-Commit-Position: refs/heads/master@{#45688}

TBR=marja@chromium.org,vogelheim@chromium.org,wiktorg@google.com
# Not skipping CQ checks because original CL landed > 1 day ago.
BUG=v8:6093

Change-Id: Iefa7c43a2f6ae3a7f3ef0f77d87b6ae36ae4be99
Reviewed-on: https://chromium-review.googlesource.com/525712Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Daniel Vogelheim <vogelheim@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45725}

include/v8.h

@@ -1284,6 +1284,11 @@ class V8_EXPORT ScriptCompiler {
      * length of the data returned. When the data ends, GetMoreData should
      * return 0. Caller takes ownership of the data.
      *
+     * When streaming UTF-8 data, V8 handles multi-byte characters split between
+     * two data chunks, but doesn't handle multi-byte characters split between
+     * more than two data chunks. The embedder can avoid this problem by always
+     * returning at least 2 bytes of data.
+     *
      * If the embedder wants to cancel the streaming, they should make the next
      * GetMoreData call return 0. V8 will interpret it as end of data (and most
      * probably, parsing will fail). The streaming task will return as soon as

test/cctest/parsing/test-scanner-streams.cc

@@ -39,13 +39,6 @@ class ChunkSource : public v8::ScriptCompiler::ExternalSourceStream {
     }
     chunks_.push_back({nullptr, 0});
   }
-  ChunkSource(const uint8_t* data, size_t len, size_t chunk_size)
-      : current_(0) {
-    for (size_t i = 0; i < len; i += chunk_size) {
-      chunks_.push_back({data + i, i::Min(chunk_size, len - i)});
-    }
-    chunks_.push_back({nullptr, 0});
-  }
   ~ChunkSource() {}
   bool SetBookmark() override { return false; }
   void ResetToBookmark() override {}
@@ -442,18 +435,6 @@ TEST(CharacterStreams) {
   TestCharacterStreams(buffer, arraysize(buffer) - 1, 576, 3298);
 }
 
-TEST(Uft8MultipleBOMChunks) {
-  const char* chunks = "\xef\xbb\xbf\0\xef\xbb\xbf\0\xef\xbb\xbf\0a\0";
-  const uint16_t unicode[] = {0xFEFF, 0xFEFF, 97};
-  ChunkSource chunk_source(chunks);
-  std::unique_ptr<i::Utf16CharacterStream> stream(i::ScannerStream::For(
-      &chunk_source, v8::ScriptCompiler::StreamedSource::UTF8, nullptr));
-  for (size_t i = 0; i < arraysize(unicode); i++) {
-    CHECK_EQ(unicode[i], stream->Advance());
-  }
-  CHECK_EQ(i::Utf16CharacterStream::kEndOfInput, stream->Advance());
-}
-
 // Regression test for crbug.com/651333. Read invalid utf-8.
 TEST(Regress651333) {
   const uint8_t bytes[] =
@@ -515,36 +496,3 @@ TEST(Regress6377) {
     CHECK_EQ(i::Utf16CharacterStream::kEndOfInput, stream->Advance());
   }
 }
-
-TEST(Regress724166) {
-  // Chunk size has to be multiple of kBufferCharacterSize
-  constexpr size_t kBufferCharacterSize = 512;
-  constexpr size_t kChunkSize = kBufferCharacterSize * 8;
-  constexpr size_t kChunks = 4;
-  uint8_t buffer[kChunkSize * kChunks];
-  for (size_t j = 0; j < kChunks; ++j) {
-    for (size_t i = 0; i < kChunkSize; ++i) {
-      buffer[kChunkSize * j + i] = (i % 0x7e) + 1;
-    }
-  }
-  // Add BOM at the beginning
-  buffer[0] = '\xef';
-  buffer[1] = '\xbb';
-  buffer[2] = '\xbf';
-  ChunkSource chunk_source(buffer, arraysize(buffer), kChunkSize);
-  std::unique_ptr<i::Utf16CharacterStream> stream(i::ScannerStream::For(
-      &chunk_source, v8::ScriptCompiler::StreamedSource::UTF8, nullptr));
-  for (size_t i = 0; i < arraysize(buffer) - 3; ++i) {
-    CHECK_EQ(static_cast<i::uc32>(buffer[i + 3]), stream->Advance());
-  }
-  CHECK_EQ(i::Utf16CharacterStream::kEndOfInput, stream->Advance());
-  for (int z = -8; z < 8; ++z) {
-    for (size_t j = kBufferCharacterSize + z; j < arraysize(buffer);
-         j += kBufferCharacterSize) {
-      stream->Seek(j);
-      for (size_t i = j; i < arraysize(buffer) - 3; ++i) {
-        CHECK_EQ(static_cast<i::uc32>(buffer[i + 3]), stream->Advance());
-      }
-    }
-  }
-}