[vm/corelib] Shrink code size of inlined _GrowableList.add

Previously, _GrowableList.add used 2 calls to grow the list which
results in extra code generated for each inlined List.add call.

This change replaces

  _grow(_nextCapacity(len));

with

  _growToNextCapacity();

which reduces code size.

Flutter gallery in release mode
instructions size -0.32% (arm), -0.1% (arm64)
total snapshot size -0.19% (arm) -0.06% (arm64)

Change-Id: I8422757d147ecec5bdec60910c65c558c39fde1d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/175006
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>

Author: alexmarkov

sdk/lib/_internal/vm/lib/growable_array.dart

@@ -261,7 +261,7 @@ class _GrowableList<T> extends ListBase<T> {
   void add(T value) {
     var len = length;
     if (len == _capacity) {
-      _grow(_nextCapacity(len));
+      _growToNextCapacity();
     }
     _setLength(len + 1);
     this[len] = value;
@@ -310,7 +310,7 @@ class _GrowableList<T> extends ListBase<T> {
         if (this.length != newLen) throw new ConcurrentModificationError(this);
         len = newLen;
       }
-      _grow(_nextCapacity(_capacity));
+      _growToNextCapacity();
     } while (true);
   }
 
@@ -370,6 +370,14 @@ class _GrowableList<T> extends ListBase<T> {
     _setData(newData);
   }
 
+  // This method is marked as never-inline to conserve code size.
+  // It is called in rare cases, but used in the add() which is
+  // used very often and always inlined.
+  @pragma("vm:never-inline")
+  void _growToNextCapacity() {
+    _grow(_nextCapacity(_capacity));
+  }
+
   void _shrink(int new_capacity, int new_length) {
     var newData = _allocateData(new_capacity);
     // This is a work-around for dartbug.com/30090. See the comment in _grow.