Precompile Document.h and LayoutObject.h for Source/web

Precompile Document.h and LayoutObject.h for Source/web

One reason Blink is slow to compile is that there is a lot of code
included in every compilation unit since everything depends on either
LayoutObject.h or Document.h and those in turn include huge portions
of the rest of Blink.

By precompiling LayoutObject.h and Document.h the compilation of core and
modules in Blink can be several times faster.

The downside is that it will introduce Document.h and LayoutObject.h
also in compilation units that didn't expect it or wanted it.

BUG=495697
R=thakis@chromium.org

[sof, 2015-06-25 07:05:21]

https://codereview.chromium.org/1178823003/diff/1/Source/web/tests/WebUnitTes...
File Source/web/tests/WebUnitTests.cpp (right):

https://codereview.chromium.org/1178823003/diff/1/Source/web/tests/WebUnitTes...
Source/web/tests/WebUnitTests.cpp:33: 
If

  #undef FROM_HERE

is added here, the expected FROM_HERE in the code below will be in scope.
Slightly tidier; you won't have to touch WebTraceLocation.h.

[Daniel Bratell, 2015-07-14 16:36:18]

bratell@opera.com changed reviewers:
+ thakis@chromium.org

[Daniel Bratell, 2015-07-14 16:36:18]

thakis, this is the last of the three major parts of Blink that can benefit from
precompiled headers.

The only tricky part here is the collision between base FROM_HERE and Blink's
almost similar FROM_HERE macro.

I don't have current numbers, but back when sof suggested this, it saved another
5 minutes (for i7 4790 computers).

[sof, 2015-07-16 07:39:11]

sigbjornf@opera.com changed reviewers:
+ sigbjornf@opera.com

[sof, 2015-07-16 07:39:12]

lgtm (but no web/ owner)

[sof, 2015-07-16 13:04:51]

Local numbers: 13:10 to rebuild(*) Blink ToT; 09:55 with this CL.

* - triggered by modifying Source/config.h

[Daniel Bratell, 2015-07-16 13:40:05]

bratell@opera.com changed reviewers:
+ jochen@chromium.org

[Daniel Bratell, 2015-07-16 13:40:05]

Jochen, could you take a look please? It's about expanding the precompiling to
one more part of Blink.

[jochen (gone - plz use gerrit), 2015-07-16 13:46:55]

https://codereview.chromium.org/1178823003/diff/60001/Source/web/WebKit.cpp
File Source/web/WebKit.cpp (right):

https://codereview.chromium.org/1178823003/diff/60001/Source/web/WebKit.cpp#n...
Source/web/WebKit.cpp:70: namespace helpers {
why this change?

[Daniel Bratell, 2015-07-16 13:57:12]

https://codereview.chromium.org/1178823003/diff/60001/Source/web/WebKit.cpp
File Source/web/WebKit.cpp (right):

https://codereview.chromium.org/1178823003/diff/60001/Source/web/WebKit.cpp#n...
Source/web/WebKit.cpp:70: namespace helpers {
On 2015/07/16 13:46:54, jochen wrote:
> why this change?

Via the precompiled headers (Document.h I assume) this code got to see the
definition of MainThreadTaskRunner in core/dom/MainThreadTaskRunner.h.

So this is just to avoid that name conflict. Other solutions are possible and if
you prefer a different way I'm perfectly fine with that.

[jochen (gone - plz use gerrit), 2015-07-16 13:58:57]

lgtm

[Daniel Bratell, 2015-07-16 14:12:54]

The CQ bit was checked by bratell@opera.com

[commit-bot: I haz the power, 2015-07-16 14:13:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1178823003/60001

[Daniel Bratell, 2015-07-16 15:15:36]

The CQ bit was unchecked by bratell@opera.com