SkSize can be aggregate-initialized

Previosly, SkSize had a base class, which prevented it.

Also removes unused SkISize::clampNegToZero() and
SkSize::clampNegToZero().

Change-Id: I7b93b42f6f6381c66e294bbedee99ad53c6c3436
Reviewed-on: https://skia-review.googlesource.com/13187
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/tests/SizeTest.cpp b/tests/SizeTest.cpp
index 9800aa2..9dccdeb 100644
--- a/tests/SizeTest.cpp
+++ b/tests/SizeTest.cpp
@@ -16,7 +16,7 @@
     REPORTER_ASSERT(reporter, a.isEmpty());
     a.set(5, -5);
     REPORTER_ASSERT(reporter, a.isEmpty());
-    a.clampNegToZero();
+    a = SkISize{5, 0};
     REPORTER_ASSERT(reporter, a.isEmpty());
     b.set(5, 0);
     REPORTER_ASSERT(reporter, a == b);
@@ -42,7 +42,7 @@
     REPORTER_ASSERT(reporter, a.isEmpty());
     a.set(x, -x);
     REPORTER_ASSERT(reporter, a.isEmpty());
-    a.clampNegToZero();
+    a = SkSize{x, 0};
     REPORTER_ASSERT(reporter, a.isEmpty());
     b.set(x, 0);
     REPORTER_ASSERT(reporter, a == b);