Add shared bitmap managers for browser and renderer processes.

cc/resources/shared_bitmap.cc

Index: cc/resources/shared_bitmap.cc
diff --git a/cc/resources/shared_bitmap.cc b/cc/resources/shared_bitmap.cc
index 3a6fc3589e3a8471b9a4d10e75278c76bfbe0a41..943f6e12c2924e15700ced7dff52e0c8bc36959f 100644
--- a/cc/resources/shared_bitmap.cc
+++ b/cc/resources/shared_bitmap.cc
@@ -4,6 +4,8 @@
 
 #include "cc/resources/shared_bitmap.h"
 
+#include "base/rand_util.h"
+
 namespace cc {
 
 SharedBitmap::SharedBitmap(
@@ -14,4 +16,17 @@ SharedBitmap::SharedBitmap(
 
 SharedBitmap::~SharedBitmap() { free_callback_.Run(this); }
 
+// static
+size_t SharedBitmap::GetSizeInBytes(const gfx::Size& size) {
+  return size.GetArea() * 4;
+}
+
+// static
+SharedBitmapId SharedBitmap::GenerateId() {
+  SharedBitmapId id;
+  // Needs cryptographically-secure random numbers.
+  base::RandBytes(id.name, sizeof(id.name));
+  return id;
+}
+
 }  // namespace cc