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..ce566709a7d7bd480e9aa75978bd4390217a568f 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"
@@ -24,12 +25,23 @@ class CC_EXPORT Resource {
   ResourceFormat format() const { return format_; }
   size_t bytes() const;

[danakj, 2015/06/04 20:58:44]

we should remove this function.

 
-  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);
+  // Return true if the call to UncheckedMemorySizeBytes would return a value
+  // that fits in a size_t.
+  static bool VerifySizeInBytes(const gfx::Size& size, ResourceFormat format) {
+    if (((BitsPerPixel(format) * size.width() * size.height()) % 8) != 0)

[danakj, 2015/06/04 20:58:43]

can you do this only if result.IsValid() and convert these to size_t's instead
of multiplying ints?

+      return false;
+    base::CheckedNumeric<size_t> result = BitsPerPixel(format);
+    result *= size.width();
+    result *= size.height();
+    result /= 8;
+    return result.IsValid();
+  }
+
+  inline static size_t UncheckedMemorySizeBytes(const gfx::Size& size,
+                                                ResourceFormat format) {
+    DCHECK(VerifySizeInBytes(size, format));
+    return static_cast<size_t>(BitsPerPixel(format)) * size.width() *
+           size.height() / 8;
   }
 
  protected: