cc: Use CheckedNumeric for resource size calculations.

cc/resources/resource.h

Index: cc/resources/resource.h
diff --git a/cc/resources/resource.h b/cc/resources/resource.h
index 0e3c3df688387b9ee927f150737bc8dd37a7a6b7..06893fe32749dad1a8d960302dcd80347b065316 100644
--- a/cc/resources/resource.h
+++ b/cc/resources/resource.h
@@ -5,6 +5,7 @@
 #ifndef CC_RESOURCES_RESOURCE_H_
 #define CC_RESOURCES_RESOURCE_H_
 
+#include "base/numerics/safe_math.h"
 #include "cc/base/cc_export.h"
 #include "cc/resources/resource_provider.h"
 #include "ui/gfx/geometry/size.h"
@@ -27,9 +28,11 @@ class CC_EXPORT Resource {
   inline static size_t MemorySizeBytes(const gfx::Size& size,
                                        ResourceFormat format) {
     DCHECK_EQ(0, (BitsPerPixel(format) * size.width() * size.height()) % 8);
-    // TODO(vmpstr): Make this function overflow safe. crbug.com/495867
-    return static_cast<size_t>(
-        (BitsPerPixel(format) * size.width() * size.height()) / 8);
+    base::CheckedNumeric<size_t> result = BitsPerPixel(format);
+    result *= size.width();
+    result *= size.height();
+    result /= 8;
+    return result.ValueOrDie();

[danakj, 2015/06/04 19:02:38]

This would work, but looking at the callsites of MemorySizeBytes, these are all
for tiles. So they are limited sizes determined by us, and not from arbitrary
inputs.

If I was to duplicate the pattern from SharedBitmap here, I'd make 2 methods:

size_t UncheckedSizeInBytes(..)
bool VerifySizeInBytes(..)

And I'd DCHECK(VerifySizeInBytes(..)) and comment explaining why the size is
controlled at the callsites of UncheckedSizeInBytes.

   }
 
  protected: