Mark mojom types which must be stable as [Stable]

Several mojom types are required to be stable over time by virtue of
their use in Content's page state serialization code.

Now that we have the [Stable] attribute with strict presubmit
enforcement, these types can all be marked [Stable] to ensure that they
aren't unwittingly broken by future changes.

Bug: 1070663
Change-Id: I7de41133eb8244f7dd8562fa713b6ad702c04ccb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2220251
Commit-Queue: Ken Rockot <rockot@google.com>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773321}

content/common/page_state.mojom

@@ -15,17 +15,16 @@ import "ui/gfx/geometry/mojom/geometry.mojom";
 // parts. The resultant generated code is used to serialize and deserialize
 // PageState for the purpose of history restore.
 //
-// When adding fields:
+// All structures here must maintain backward-compatibility (and hence must be
+// marked [Stable]) according to mojom backward-compatibility rules. Namely,
+// when adding new fields:
 // - Assign your new field an explicit ordinal(@n) and prefer to add fields to
 //   the end of the struct to simplify finding the latest ordinal.
-// - For backwards compatibility purposes:
-//     - New fields must be tagged with a [MinVersion=x] attribute; x is
-//       specified at the bottom of this comment block.
-//     - Only types with frozen/unchanging Mojo serialization may be used;
-//       for example, |string| is okay, but |url.mojom.Origin| is not.
-//       (note that if serialization of any of the types used in PageState
-//       changes in a backwards-incompatible way then it should be caught by
-//       one of PageStateSerializationTest, BackwardsCompat_vXX tests).
+// - New fields must be tagged with a [MinVersion=x] attribute where x is larger
+//   than the MinVersion for any existing fields. The next available MinVersion
+//   value is specified at the bottom of this comment block for convenience.
+// - Only builtin mojom types or other user-defined [Stable] types are allowed
+//   as transitive dependencies here. This is enforced at build time.
 // - You'll also need to read/write the new field's value when decoding and
 //   encoding PageState, update PageStateSerializationTest to check that your
 //   new field is preserved across serialization, and add a BackwardsCompat
@@ -37,11 +36,15 @@ import "ui/gfx/geometry/mojom/geometry.mojom";
 // compatibility. If re-ordering fields, make sure to retain the original
 // ordinal value.
 //
+// Finally, note that any backward-incomptable changes will be caught by a
+// presubmit check.
+//
 // Update the below value if your change introduces fields using it.
 // Next MinVersion: 3
 
 // Next Ordinal: 4
 // FileSystemFile is no longer supported.
+[Stable]
 struct DEPRECATED_FileSystemFile {
   url.mojom.Url filesystem_url@0;
   uint64 offset@1;
@@ -50,6 +53,7 @@ struct DEPRECATED_FileSystemFile {
 };
 
 // Next Ordinal: 4
+[Stable]
 struct File {
   mojo_base.mojom.String16 path@0;
   uint64 offset@1;
@@ -58,6 +62,7 @@ struct File {
 };
 
 // Next Ordinal: 4
+[Stable]
 union Element {
   string blob_uuid@0;
   array<uint8> bytes@1;
@@ -67,6 +72,7 @@ union Element {
 };
 
 // Next Ordinal: 3
+[Stable]
 struct RequestBody {
   array<Element> elements@0;
   int64 identifier@1;
@@ -74,6 +80,7 @@ struct RequestBody {
 };
 
 // Next Ordinal: 3
+[Stable]
 struct HttpBody {
   mojo_base.mojom.String16? http_content_type@0;
   RequestBody? request_body@1;
@@ -82,13 +89,14 @@ struct HttpBody {
 
 // This enum's values must match blink::WebHistoryScrollRestorationType. This
 // is enforced with static asserts in page_state_serialization.cc.
-[Extensible]
+[Stable, Extensible]
 enum ScrollRestorationType {
   kAuto = 0,
   kManual = 1
 };
 
 // Next Ordinal: 6
+[Stable]
 struct ViewState {
   gfx.mojom.PointF visual_viewport_scroll_offset@0;
   gfx.mojom.Point scroll_offset@1;
@@ -100,6 +108,7 @@ struct ViewState {
 };
 
 // Next Ordinal: 13
+[Stable]
 struct FrameState {
   mojo_base.mojom.String16? url_string@0;
   mojo_base.mojom.String16? referrer@1;
@@ -117,6 +126,7 @@ struct FrameState {
 };
 
 // Next Ordinal: 2
+[Stable]
 struct PageState {
   array<mojo_base.mojom.String16?> referenced_files@0;
   FrameState top@1;

mojo/public/mojom/base/string16.mojom

@@ -9,10 +9,7 @@ import "mojo/public/mojom/base/big_buffer.mojom";
 // Corresponds to |base::string16| in base/strings/string16.h
 // Corresponds to |WTF::String| in
 // third_party/WebKit/Source/platform/wtf/text/WTFString.h.
-// Don't make backwards-incompatible changes to this definition!
-// It's used in PageState serialization, so backwards incompatible changes
-// would cause stored PageState objects to be un-parseable. Please contact the
-// page state serialization owners before making such a change.
+[Stable]
 struct String16 {
   array<uint16> data;
 };

mojo/public/mojom/base/time.mojom

@@ -4,6 +4,7 @@
 
 module mojo_base.mojom;
 
+[Stable]
 struct Time {
   // The internal value is expressed in terms of microseconds since a fixed but
   // intentionally unspecified epoch.

services/network/public/mojom/referrer_policy.mojom

@@ -4,10 +4,7 @@
 
 module network.mojom;
 
-// Don't make backwards-incompatible changes to this definition!
-// It's used in PageState serialization, so backwards incompatible changes
-// would cause stored PageState objects to be un-parseable. Please contact the
-// page state serialization owners before making such a change.
+[Stable]
 enum ReferrerPolicy {
     kAlways,
     kDefault,

ui/gfx/geometry/mojom/geometry.mojom

@@ -4,18 +4,13 @@
 
 module gfx.mojom;
 
-// Don't make backwards-incompatible changes to this definition!
-// It's used in PageState serialization, so backwards incompatible changes
-// would cause stored PageState objects to be un-parseable.
+[Stable]
 struct Point {
   int32 x;
   int32 y;
 };
 
-// Don't make backwards-incompatible changes to this definition!
-// It's used in PageState serialization, so backwards incompatible changes
-// would cause stored PageState objects to be un-parseable. Please contact the
-// page state serialization owners before making such a change.
+[Stable]
 struct PointF {
   float x;
   float y;

url/mojom/url.mojom

@@ -4,10 +4,7 @@
 
 module url.mojom;
 
-// Don't make backwards-incompatible changes to this definition!
-// It's used in PageState serialization, so backwards incompatible changes
-// would cause stored PageState objects to be un-parseable. Please contact the
-// page state serialization owners before making such a change.
+[Stable]
 struct Url {
   string url;
 };