Fix the issue that it may get wrong stride in cc::ResourceProvider::MapImage.

cc/resources/resource_provider.cc

Index: cc/resources/resource_provider.cc
diff --git a/cc/resources/resource_provider.cc b/cc/resources/resource_provider.cc
index e58ed0b73b7c33c01b62ae654d8ec3bdf1664704..e1e533228cf41b1c33e325ac150030e7333c88db 100644
--- a/cc/resources/resource_provider.cc
+++ b/cc/resources/resource_provider.cc
@@ -2150,10 +2150,11 @@ uint8_t* ResourceProvider::MapImage(const Resource* resource, int* stride) {
     DCHECK(resource->image_id);
     GLES2Interface* gl = ContextGL();
     DCHECK(gl);
+    uint8_t* ret = static_cast<uint8_t*>(

[reveman, 2014/03/01 23:04:10]

nit: s/ret/pixels/

[junj, 2014/03/03 10:52:30]

Done.

+        gl->MapImageCHROMIUM(resource->image_id, GL_READ_WRITE));
     gl->GetImageParameterivCHROMIUM(
         resource->image_id, GL_IMAGE_ROWBYTES_CHROMIUM, stride);

[reveman, 2014/03/01 23:04:10]

It's not obvious that this needs to be called after map. Please add a short
comment here explaining this and a DCHECK to
GLES2Implementation::GetImageParameterivCHROMIUMHelper to guard against
incorrect usage.

[junj, 2014/03/03 10:52:30]

Done.

-    return static_cast<uint8_t*>(
-        gl->MapImageCHROMIUM(resource->image_id, GL_READ_WRITE));
+    return ret;
   }
   DCHECK_EQ(Bitmap, resource->type);
   *stride = 0;