Revert of Remove unused (by clients) SkUnitMapper (https://codereview.chromium.org/283273002/)

gyp/public_headers.gypi

 # Include this gypi to include all public header files that exist in the
 # include directory.
 #
 # The list is computed by running 'find include -name *.h' in the root dir of
 # the project.
 #
 {
   'variables': {
     'header_filenames': [
       'pdf/SkPDFDevice.h',
@@ skipping 99 matching lines @@
       'effects/SkColorFilterImageFilter.h',
       'effects/SkLayerDrawLooper.h',
       'effects/SkLightingImageFilter.h',
       'effects/SkDropShadowImageFilter.h',
       'effects/SkMatrixConvolutionImageFilter.h',
       'utils/win/SkAutoCoInitialize.h',
       'utils/win/SkHRESULT.h',
       'utils/win/SkIStream.h',
       'utils/win/SkTScopedComPtr.h',
       'utils/SkBoundaryPatch.h',
+      'utils/SkUnitMappers.h',
       'utils/SkPictureUtils.h',
       'utils/SkRandom.h',
       'utils/SkMeshUtils.h',
       'utils/SkCullPoints.h',
       'utils/SkCamera.h',
       'utils/SkLua.h',
       'utils/SkParsePaint.h',
       'utils/SkCountdown.h',
       'utils/SkRunnable.h',
       'utils/SkParse.h',
@@ skipping 120 matching lines @@
       'core/SkString.h',
       'core/SkPixelRef.h',
       'core/SkSize.h',
       'core/SkEmptyShader.h',
       'core/SkSurface.h',
       'core/SkPostConfig.h',
       'core/SkShader.h',
       'core/SkWriter32.h',
       'core/SkError.h',
       'core/SkPath.h',
+      'core/SkUnitMapper.h',
       'core/SkFlattenable.h',
       'core/SkTSearch.h',
       'core/SkRect.h',
       'pathops/SkPathOps.h',
       'views/SkTouchGesture.h',
       'views/SkEvent.h',
       'views/SkOSWindow_NaCl.h',
       'views/SkTextBox.h',
       'views/SkViewInflate.h',
       'views/SkOSWindow_iOS.h',
@@ skipping 16 matching lines @@
       'views/unix/XkeysToSkKeys.h',
       'views/SkKey.h',
       'views/SkView.h',
       'views/SkOSMenu.h',
       'views/SkOSWindow_Unix.h',
       'views/SkWidget.h',
       'views/SkOSWindow_Win.h',
     ],
   },
 }