Use the correct homophone of 'there'.

include/core/SkBitmap.h

Index: include/core/SkBitmap.h
diff --git a/include/core/SkBitmap.h b/include/core/SkBitmap.h
index a6acb8713e4bc04aaac4cc565cb24d7249dd3330..35f0151430bdc87d8be334c0c97b6d69b80fe43c 100644
--- a/include/core/SkBitmap.h
+++ b/include/core/SkBitmap.h
@@ -500,7 +500,7 @@ public:
     /** Returns a non-zero, unique value corresponding to the pixels in our
         pixelref. Each time the pixels are changed (and notifyPixelsChanged
         is called), a different generation ID will be returned. Finally, if
-        their is no pixelRef then zero is returned.
+        there is no pixelRef then zero is returned.
     */
     uint32_t getGenerationID() const;