[asm] Remove invalid static cast of character stream

TBR=ahaas@chromium.org

Change-Id: I862cae063d85703235ead073b0f23515721a409f
Reviewed-on: https://chromium-review.googlesource.com/1181431
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55226}

src/asmjs/asm-parser.cc

@@ -71,7 +71,7 @@ namespace wasm {
 AsmJsParser::AsmJsParser(Zone* zone, uintptr_t stack_limit,
                          ScannerStream* stream, int start)
     : zone_(zone),
-      scanner_(static_cast<CharacterStream<uint16_t>*>(stream), start),
+      scanner_(stream, start),
       module_builder_(new (zone) WasmModuleBuilder(zone)),
       return_type_(nullptr),
       stack_limit_(stack_limit),

test/unittests/asmjs/asm-scanner-unittest.cc

@@ -17,8 +17,7 @@ class AsmJsScannerTest : public ::testing::Test {
  protected:
   void SetupScanner(const char* source) {
     stream = ScannerStream::ForTesting(source);
-    scanner.reset(new AsmJsScanner(
-        static_cast<CharacterStream<uint16_t>*>(stream.get()), 0));
+    scanner.reset(new AsmJsScanner(stream.get(), 0));
   }
 
   void Skip(AsmJsScanner::token_t t) {