revise SkTDynamicHash and add unit tests

gyp/tests.gyp

 # GYP file to build unit tests.
 {
   'includes': [
     'apptype_console.gypi',
   ],
   'targets': [
     {
       'target_name': 'tests',
       'type': 'executable',
       'include_dirs' : [
@@ skipping 30 matching lines @@
         '../tests/ClipStackTest.cpp',
         '../tests/ClipperTest.cpp',
         '../tests/ColorFilterTest.cpp',
         '../tests/ColorTest.cpp',
         '../tests/DataRefTest.cpp',
         '../tests/DeferredCanvasTest.cpp',
         '../tests/DequeTest.cpp',
         '../tests/DrawBitmapRectTest.cpp',
         '../tests/DrawPathTest.cpp',
         '../tests/DrawTextTest.cpp',
+        '../tests/DynamicHashTest.cpp',
         '../tests/EmptyPathTest.cpp',
         '../tests/ErrorTest.cpp',
         '../tests/FillPathTest.cpp',
         '../tests/FitsInTest.cpp',
         '../tests/FlatDataTest.cpp',
         '../tests/FlateTest.cpp',
         '../tests/FontHostStreamTest.cpp',
         '../tests/FontHostTest.cpp',
         '../tests/FontMgrTest.cpp',
         '../tests/FontNamesTest.cpp',
@@ skipping 99 matching lines @@
       ],
     },
   ],
 }
 
 # Local Variables:
 # tab-width:2
 # indent-tabs-mode:nil
 # End:
 # vim: set expandtab tabstop=2 shiftwidth=2: