unsigned -> int for counts and indices in picture-related code

also, (C)

BUG=skia:

Review URL: https://codereview.chromium.org/1300163002
diff --git a/tests/RecordDrawTest.cpp b/tests/RecordDrawTest.cpp
index da78296..84ceb20 100644
--- a/tests/RecordDrawTest.cpp
+++ b/tests/RecordDrawTest.cpp
@@ -126,17 +126,17 @@
     void insert(const SkRect boundsArray[], int N) override {
         fEntries.setCount(N);
         for (int i = 0; i < N; i++) {
-            Entry e = { (unsigned)i, boundsArray[i] };
+            Entry e = { i, boundsArray[i] };
             fEntries[i] = e;
         }
     }
 
-    void search(const SkRect& query, SkTDArray<unsigned>* results) const override {}
+    void search(const SkRect& query, SkTDArray<int>* results) const override {}
     size_t bytesUsed() const override { return 0; }
     SkRect getRootBound() const override { return SkRect::MakeEmpty(); }
 
     struct Entry {
-        unsigned opIndex;
+        int opIndex;
         SkRect bounds;
     };
     SkTDArray<Entry> fEntries;
@@ -166,7 +166,7 @@
 
     REPORTER_ASSERT(r, bbh.fEntries.count() == 5);
     for (int i = 0; i < bbh.fEntries.count(); i++) {
-        REPORTER_ASSERT(r, bbh.fEntries[i].opIndex == (unsigned)i);
+        REPORTER_ASSERT(r, bbh.fEntries[i].opIndex == i);
 
         REPORTER_ASSERT(r, sloppy_rect_eq(SkRect::MakeWH(400, 480), bbh.fEntries[i].bounds));
     }