[cleanup] Make Add() out-of-line in ExternalReferenceTable.

We call this ~140 times from addReferences() and AddStubCache, which
caused size to increase.

Bug: 
Change-Id: Ib08d435abb82b3e07121adf023f96f6f0b33733e
Reviewed-on: https://chromium-review.googlesource.com/660120Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47949}

src/external-reference-table.cc

@@ -60,6 +60,10 @@ const char* ExternalReferenceTable::ResolveSymbol(void* address) {
 #endif  // SYMBOLIZE_FUNCTION
 }
 
+void ExternalReferenceTable::Add(Address address, const char* name) {
+  refs_.emplace_back(address, name);
+}
+
 void ExternalReferenceTable::AddReferences(Isolate* isolate) {
   // Miscellaneous
   Add(ExternalReference::roots_array_start(isolate).address(),

src/external-reference-table.h

@@ -32,14 +32,14 @@ class ExternalReferenceTable {
   struct ExternalReferenceEntry {
     Address address;
     const char* name;
+
+    ExternalReferenceEntry(Address address, const char* name)
+        : address(address), name(name) {}
   };
 
   explicit ExternalReferenceTable(Isolate* isolate);
 
-  void Add(Address address, const char* name) {
-    ExternalReferenceEntry entry = {address, name};
-    refs_.push_back(entry);
-  }
+  void Add(Address address, const char* name);
 
   void AddReferences(Isolate* isolate);
   void AddBuiltins(Isolate* isolate);