Align all SkRecord::alloc() calls up to at least a pointer size.

This should make the LSAN bots able to see all our pointers.

BUG=skia:
R=reed@google.com, robertphillips@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/517073002

include/core/SkTypes.h

@@ -300,6 +300,9 @@ static inline bool SkIsU16(long x) {
 #define SkAlign8(x)     (((x) + 7) >> 3 << 3)
 #define SkIsAlign8(x)   (0 == ((x) & 7))
 
+#define SkAlignPtr(x)   (sizeof(void*) == 8 ?   SkAlign8(x) :   SkAlign4(x))
+#define SkIsAlignPtr(x) (sizeof(void*) == 8 ? SkIsAlign8(x) : SkIsAlign4(x))
+
 typedef uint32_t SkFourByteTag;
 #define SkSetFourByteTag(a, b, c, d)    (((a) << 24) | ((b) << 16) | ((c) << 8) | (d))
 

src/core/SkRecord.h

@@ -65,7 +65,8 @@ public:
     // Here T can be any class, not just those from SkRecords.  Throws on failure.
     template <typename T>
     T* alloc(size_t count = 1) {
-        return (T*)fAlloc.allocThrow(sizeof(T) * count);
+        // Bump up to the next pointer width if needed, so all allocations start pointer-aligned.
+        return (T*)fAlloc.allocThrow(SkAlignPtr(sizeof(T) * count));
     }
 
     // Add a new command of type T to the end of this SkRecord.

tests/RecordTest.cpp

@@ -78,3 +78,28 @@ DEF_TEST(Record, r) {
 
 #undef APPEND
 
+template <typename T>
+static bool is_aligned(const T* p) {
+    return (((uintptr_t)p) & (sizeof(T) - 1)) == 0;
+}
+
+DEF_TEST(Record_Alignment, r) {
+    SkRecord record;
+
+    // Of course a byte's always aligned.
+    REPORTER_ASSERT(r, is_aligned(record.alloc<uint8_t>()));
+
+    // (If packed tightly, the rest below here would be off by one.)
+
+    // It happens that the first implementation always aligned to 4 bytes,
+    // so these two were always correct.
+    REPORTER_ASSERT(r, is_aligned(record.alloc<uint16_t>()));
+    REPORTER_ASSERT(r, is_aligned(record.alloc<uint32_t>()));
+
+    // These two are regression tests (void* only on 64-bit machines).
+    REPORTER_ASSERT(r, is_aligned(record.alloc<uint64_t>()));
+    REPORTER_ASSERT(r, is_aligned(record.alloc<void*>()));
+
+    // We're not testing beyond sizeof(void*), which is where the current implementation will break.
+}
+