devtools: Make Tracing.start asynchronous

Internally, Chrome tracing needs to be enabled for every Chrome process,
so it is done asynchronously. Make the associated Tracing.start message
asynchronous so it can signal completion at a later point in time.

BUG=307841

Review URL: https://codereview.chromium.org/134253002

git-svn-id: svn://svn.chromium.org/blink/trunk@164990 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: [Styles] Improve UI for toggling computed inherited properties display

Drive-by: Make the Computed pane background white (even though the section is read-only)

R=aandrey, eustas, vsevik
BUG=333844

Review URL: https://codereview.chromium.org/130803003

git-svn-id: svn://svn.chromium.org/blink/trunk@164991 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Rebaseline Skia suppressions.

BUG=314499,326138,329201,331781
TBR=robert.phillips@google.com

Review URL: https://codereview.chromium.org/136913002

git-svn-id: svn://svn.chromium.org/blink/trunk@164992 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[CSS Shapes] Shape images are now image types, not just URIs

This change supports potentially-CORS-enabled loading of image-set elements by shape-inside and shape-outside.

The changes to CSSImageSetValue are analogous to the ones I made in https://codereview.chromium.org/40653002 for CSSImageValue.

The StyleResourceLoader change is slightly awkward to preserve StyleResourceLoader.h's low-impact #include list. I didn't make doLoadPendingImage() (nee loadPendingImage) a private method to avoid the dependency on the CORSEnabled enum, which is defined in ResourceFetcher.h.

BUG=328180

Review URL: https://codereview.chromium.org/128623004

git-svn-id: svn://svn.chromium.org/blink/trunk@164993 bbb929c8-8fbe-4397-9dbb-9b2b20218538