Update libwebp to v0.5.2-rc2

This matches the version used by Chromium (crbug.com/675306) and
Android (https://android-review.googlesource.com/#/c/316352/).

Update our test. In the new version, we successfully decode a subset
from incomplete input that we previously did not.

Change-Id: I3442bf59ffdf223a723d8aa75f5b9b816b9e9c3c
Reviewed-on: https://skia-review.googlesource.com/6320
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
diff --git a/tests/CodecTest.cpp b/tests/CodecTest.cpp
index 19494b2..01e9cc4 100644
--- a/tests/CodecTest.cpp
+++ b/tests/CodecTest.cpp
@@ -387,7 +387,13 @@
                                                         &opts, nullptr, nullptr);
 
         if (supportsSubsetDecoding) {
-            REPORTER_ASSERT(r, result == expectedResult);
+            if (expectedResult == SkCodec::kSuccess) {
+                REPORTER_ASSERT(r, result == expectedResult);
+            } else {
+                SkASSERT(expectedResult == SkCodec::kIncompleteInput);
+                REPORTER_ASSERT(r, result == SkCodec::kIncompleteInput
+                                || result == SkCodec::kSuccess);
+            }
             // Webp is the only codec that supports subsets, and it will have modified the subset
             // to have even left/top.
             REPORTER_ASSERT(r, SkIsAlign2(subset.fLeft) && SkIsAlign2(subset.fTop));