[parsing] Fix bug in rewriter concerning a breakable try-finally.

R=adamk@chromium.org

Bug: chromium:787698
Change-Id: I873debe61b152a9e88ce22d95a69f27eab2d0f55
Reviewed-on: https://chromium-review.googlesource.com/787473Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49653}

src/parsing/rewriter.cc

@@ -263,6 +263,9 @@ void Processor::VisitTryFinallyStatement(TryFinallyStatement* node) {
         0, factory()->NewExpressionStatement(save, kNoSourcePosition), zone());
     node->finally_block()->statements()->Add(
         factory()->NewExpressionStatement(restore, kNoSourcePosition), zone());
+    // We can't tell whether the finally-block is guaranteed to set .result, so
+    // reset is_set_ before visiting the try-block.
+    is_set_ = false;
   }
   Visit(node->try_block());
   node->set_try_block(replacement_->AsBlock());

test/mjsunit/es6/completion.js

@@ -169,3 +169,10 @@ assertUndef(eval(
 assertUndef(eval("1; try{2; throwOnReturn();} catch(e){}"));
 assertUndef(eval("1; twoFunc();"));
 assertEquals(2, eval("1; with ( { a: 0 } ) { 2; }"));
+
+// https://bugs.chromium.org/p/chromium/issues/detail?id=787698
+assertEquals(42, eval("try {42} catch (_) {} finally {}"));
+assertEquals(42, eval("try {42} catch (_) {} finally {43}"));
+assertEquals(42, eval("foo: try {42} catch (_) {} finally {}"));
+assertEquals(42, eval("foo: try {42} catch (_) {} finally {43}"));
+assertEquals(43, eval("foo: try {42} catch (_) {} finally {43; break foo}"));