Return Object* instead of MaybeObject* from runtime calls.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 0d884303b152042da7a477daa67aca0af557a57b..6628a80a3d99d07698576af08e72b0d45b2202d8 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -2499,6 +2499,9 @@ bool Heap::CreateInitialMaps() {
   Oddball::cast(obj)->set_kind(Oddball::kUndefined);
   ASSERT(!InNewSpace(undefined_value()));
 
+  // Set preliminary exception sentinel value before actually initializing it.
+  set_exception(null_value());
+
   // Allocate the empty descriptor array.
   { MaybeObject* maybe_obj = AllocateEmptyFixedArray();
     if (!maybe_obj->ToObject(&obj)) return false;
@@ -3972,7 +3975,9 @@ MaybeObject* Heap::AllocateStringFromUtf8Slow(Vector<const char> string,
   {
     int chars = non_ascii_start + utf16_length;
     MaybeObject* maybe_result = AllocateRawTwoByteString(chars, pretenure);
-    if (!maybe_result->ToObject(&result)) return maybe_result;
+    if (!maybe_result->ToObject(&result) || result->IsException()) {
+      return maybe_result;
+    }
   }
   // Convert and copy the characters into the new object.
   SeqTwoByteString* twobyte = SeqTwoByteString::cast(result);
@@ -3999,11 +4004,15 @@ MaybeObject* Heap::AllocateStringFromTwoByte(Vector<const uc16> string,
 
   if (String::IsOneByte(start, length)) {
     MaybeObject* maybe_result = AllocateRawOneByteString(length, pretenure);
-    if (!maybe_result->ToObject(&result)) return maybe_result;
+    if (!maybe_result->ToObject(&result) || result->IsException()) {
+      return maybe_result;
+    }
     CopyChars(SeqOneByteString::cast(result)->GetChars(), start, length);
   } else {  // It's not a one byte string.
     MaybeObject* maybe_result = AllocateRawTwoByteString(length, pretenure);
-    if (!maybe_result->ToObject(&result)) return maybe_result;
+    if (!maybe_result->ToObject(&result) || result->IsException()) {
+      return maybe_result;
+    }
     CopyChars(SeqTwoByteString::cast(result)->GetChars(), start, length);
   }
   return result;