Add a class to allocate small objects w/o extra calls to new.

gyp/tests.gypi

Index: gyp/tests.gypi
diff --git a/gyp/tests.gypi b/gyp/tests.gypi
index f5143e202837386e404c351be9733effb33b773a..57b301b1e1bb86713fd95bb642df9b0ed724c782 100644
--- a/gyp/tests.gypi
+++ b/gyp/tests.gypi
@@ -1,3 +1,4 @@
+# Common gypi for unit tests.
 {
   'include_dirs': [
     '../src/core',
@@ -145,6 +146,7 @@
     '../tests/SkBase64Test.cpp',
     '../tests/SortTest.cpp',
     '../tests/SrcOverTest.cpp',
+    '../tests/StackAllocatorTest.cpp',
     '../tests/StreamTest.cpp',
     '../tests/StringTest.cpp',
     '../tests/StrokeTest.cpp',