Enable emplace_back for zone containers

As required by C++11, this CL changes the zone allocator to be able to
construct and destroy arbitrary types, and accept arbitrary arguments
for construct, passing them via perfect forwarding.
I also change some push_back to emplace_back. Some of those did not
compile before.

R=ishell@chromium.org, titzer@chromium.org

Review-Url: https://codereview.chromium.org/2646873004
Cr-Commit-Position: refs/heads/master@{#42597}

src/wasm/module-decoder.cc

@@ -1201,7 +1201,7 @@ FunctionOffsetsResult DecodeWasmFunctionOffsets(const byte* module_start,
   for (uint32_t i = 0; i < functions_count && decoder.ok(); ++i) {
     uint32_t size = decoder.consume_u32v("body size");
     int offset = static_cast<int>(section_offset + decoder.pc_offset());
-    table.push_back(std::make_pair(offset, static_cast<int>(size)));
+    table.emplace_back(offset, static_cast<int>(size));
     DCHECK(table.back().first >= 0 && table.back().second >= 0);
     decoder.consume_bytes(size);
   }
@@ -1224,7 +1224,7 @@ AsmJsOffsetsResult DecodeAsmJsOffsets(const byte* tables_start,
   for (uint32_t i = 0; i < functions_count && decoder.ok(); ++i) {
     uint32_t size = decoder.consume_u32v("table size");
     if (size == 0) {
-      table.push_back(std::vector<AsmJsOffsetEntry>());
+      table.emplace_back();
       continue;
     }
     if (!decoder.checkAvailable(size)) {

src/wasm/wasm-interpreter.cc

@@ -1789,7 +1789,7 @@ class WasmInterpreterInternals : public ZoneObject {
         codemap_(env.instance ? env.instance->module : nullptr,
                  module_bytes_.data(), zone),
         threads_(zone) {
-    threads_.push_back(ThreadImpl(zone, &codemap_, env.instance));
+    threads_.emplace_back(zone, &codemap_, env.instance);
   }
 
   void Delete() { threads_.clear(); }

src/wasm/wasm-text.cc

@@ -90,8 +90,7 @@ void wasm::PrintWasmText(const WasmModule *module,
     const int kMaxIndentation = 64;
     int indentation = std::min(kMaxIndentation, 2 * control_depth);
     if (offset_table) {
-      offset_table->push_back(debug::WasmDisassemblyOffsetTableEntry(
-          i.pc_offset(), line_nr, indentation));
+      offset_table->emplace_back(i.pc_offset(), line_nr, indentation);
     }
 
     // 64 whitespaces

src/zone/zone-allocator.h

@@ -49,10 +49,15 @@ class zone_allocator {
   size_type max_size() const throw() {
     return std::numeric_limits<int>::max() / sizeof(value_type);
   }
-  void construct(pointer p, const T& val) {
-    new (static_cast<void*>(p)) T(val);
+  template <typename U, typename... Args>
+  void construct(U* p, Args&&... args) {
+    void* v_p = const_cast<void*>(static_cast<const void*>(p));
+    new (v_p) U(std::forward<Args>(args)...);
+  }
+  template <typename U>
+  void destroy(U* p) {
+    p->~U();
   }
-  void destroy(pointer p) { p->~T(); }
 
   bool operator==(zone_allocator const& other) const {
     return zone_ == other.zone_;