Mojo: Convert scoped_ptr<...>() to nullptr in mojo/embedder.

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/606143003

Cr-Commit-Position: refs/heads/master@{#297093}

mojo/embedder/simple_platform_shared_buffer.cc

@@ -52,7 +52,7 @@ scoped_ptr<PlatformSharedBufferMapping> SimplePlatformSharedBuffer::Map(
     size_t offset,
     size_t length) {
   if (!IsValidMap(offset, length))
-    return scoped_ptr<PlatformSharedBufferMapping>();
+    return nullptr;
 
   return MapNoCheck(offset, length);
 }

mojo/embedder/simple_platform_shared_buffer_posix.cc

@@ -137,7 +137,7 @@ scoped_ptr<PlatformSharedBufferMapping> SimplePlatformSharedBuffer::MapImpl(
   // return null either.
   if (real_base == MAP_FAILED || !real_base) {
     PLOG(ERROR) << "mmap";
-    return scoped_ptr<PlatformSharedBufferMapping>();
+    return nullptr;
   }
 
   void* base = static_cast<char*>(real_base) + offset_rounding;

mojo/embedder/simple_platform_shared_buffer_win.cc

@@ -75,7 +75,7 @@ scoped_ptr<PlatformSharedBufferMapping> SimplePlatformSharedBuffer::MapImpl(
                                   real_length);
   if (!real_base) {
     PLOG(ERROR) << "MapViewOfFile";
-    return scoped_ptr<PlatformSharedBufferMapping>();
+    return nullptr;
   }
 
   void* base = static_cast<char*>(real_base) + offset_rounding;