Shape across HarfBuzz runs

Shape across HarfBuzz runs

Change HarfBuzzShaper to shape text across HarfBuzzRuns. This allows
for better handling of zero width joiners and is the first step towards
supporting shaping across elements.

Must land after change 167703008 as without that change it will cache
incorrect information due to the text string value no longer being
sufficient as shaping now includes contextual information from adjacent
runs.

R=behdad@chromium.org,leviw@chromium.org
BUG=345401
TEST=PerformanceTests/Layout/hindi-line-layout.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=180470

[behdad_google, 2014-08-15 22:45:42]

lgtm

[leviw_travelin_and_unemployed, 2014-08-15 23:01:47]

Make a comment in the description about waiting for the other patch to land and
why, and lgtm.

[leviw_travelin_and_unemployed, 2014-08-15 23:02:04]

(Also, I wish we had unit tests for this...)

[eae, 2014-08-15 23:02:34]

On 2014/08/15 23:02:04, leviw wrote:
> (Also, I wish we had unit tests for this...)

We do have layout tests for this.

[eae, 2014-08-18 15:22:42]

The CQ bit was checked by eae@chromium.org

[commit-bot: I haz the power, 2014-08-18 15:22:56]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/eae@chromium.org/478823003/20001

[commit-bot: I haz the power, 2014-08-18 15:53:15]

Committed patchset #2 (20001) as 180470