wasm: implemente WasmFrame::cast, fix inheritance

src/frames.h

Index: src/frames.h
diff --git a/src/frames.h b/src/frames.h
index ccf069c8c1322dec4002ded85b47880a60064626..466c850e0a6a7cff0b991550f758f5f1b5a6995b 100644
--- a/src/frames.h
+++ b/src/frames.h
@@ -414,7 +414,9 @@ class StackFrame BASE_EMBEDDED {
   bool is_exit() const { return type() == EXIT; }
   bool is_optimized() const { return type() == OPTIMIZED; }
   bool is_interpreted() const { return type() == INTERPRETED; }
-  bool is_wasm() const { return type() == WASM; }
+  bool is_wasm() const {

[bradn, 2016/03/28 23:46:06]

Keeping the 3 sorts of wasm frames orthogonal seems clearer to me.

[JF, 2016/03/29 00:24:06]

I don't mind either way, but if we keep them separate then they probably
shouldn't inherit from WasmFrame. I'm simply mimicking what JavaScriptFrame does
with OptimizedFrame and InterpretedFrame deriving from JavaScriptFrame, and
is_java_script() returning true if it's one of those 3 types.

+    return type() == WASM || is_wasm_to_js() || is_js_to_wasm();
+  }
   bool is_wasm_to_js() const { return type() == WASM_TO_JS; }
   bool is_js_to_wasm() const { return type() == JS_TO_WASM; }
   bool is_arguments_adaptor() const { return type() == ARGUMENTS_ADAPTOR; }
@@ -961,6 +963,11 @@ class WasmFrame : public StandardFrame {
   // Determine the code for the frame.
   Code* unchecked_code() const override;
 
+  static WasmFrame* cast(StackFrame* frame) {
+    DCHECK(frame->is_wasm());

[bradn, 2016/03/28 23:46:06]

Why not preserve the existing categories and dcheck or of all 3 here?

+    return static_cast<WasmFrame*>(frame);
+  }
+
  protected:
   inline explicit WasmFrame(StackFrameIteratorBase* iterator);