Make content::ResourceType an enum class.

This allows us to be more explicit when content::ResourceType needs to
be smuggled in an untyped int. It has the effect of introducing more
static_cast<int>, but this makes the conversion sites explicit.

This also allows several other incidental fixes:
- the Mojo version of the enum no longer defines a sentinel value (which
  violates best practices in the security guidelines)
- the C++ version of the enum can now define a compiler-enforced
  kMaxValue enumerator.
- Since kMaxValue is no longer a distinct value, dummy handling for this
  value can be removed. This revealed a quirk in
  chrome/browser/predictors/loading_data_collector.cc

Tbr: [email protected]
Tbr: [email protected]
Tbr: [email protected]
Tbr: [email protected]
Change-Id: I7203a029b1fcb06426c957d208e9278a25d4a45b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1569345
Commit-Queue: Daniel Cheng <[email protected]>
Reviewed-by: Bo <[email protected]>
Reviewed-by: Tom Sepez <[email protected]>
Reviewed-by: Matt Menke <[email protected]>
Cr-Commit-Position: refs/heads/master@{#652395}
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index c319c1a..1491bf58 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -4498,7 +4498,7 @@
                                                              top_frame_origin);
     } else {
       scoped_refptr<net::URLRequestContextGetter> request_context(
-          resource_type == RESOURCE_TYPE_MEDIA
+          resource_type == ResourceType::kMedia
               ? partition->GetMediaURLRequestContext()
               : partition->GetURLRequestContext());
       base::PostTaskWithTraits(