Replace forward declaration with include in default_component_installer.h

Replace forward declaration with include in default_component_installer.h

Because the "DictionaryValue" type is used in a scoped_ptr and scoped_ptr needs
to invoke the destructor, the full definition of the class is needed at compile
time. We apparently get lucky with include order on the non-Windows platforms,
because this only showed up when adding a new transitive dependency upon
default_component_installer.h and then only failed on Windows.

Fixing this unblocks the unconditional inclusion of the
cld_component_installer, which we need in order to fix crbug/367239.

BUG=
TBR=waffles@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=286200

[anton1, 2014-07-29 10:57:46]

lgtm

[Andrew Hayden (chromium.org), 2014-07-29 11:01:28]

The CQ bit was checked by andrewhayden@chromium.org

[commit-bot: I haz the power, 2014-07-29 11:03:25]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/andrewhayden@chromium.org/422253002/1

[commit-bot: I haz the power, 2014-07-29 12:54:54]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_chromium_chromeos_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  win_chromium_compile_dbg on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_comp...)

[commit-bot: I haz the power, 2014-07-29 14:07:37]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-07-29 14:07:38]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[Andrew Hayden (chromium.org), 2014-07-29 14:11:24]

The CQ bit was checked by andrewhayden@chromium.org

[commit-bot: I haz the power, 2014-07-29 14:12:13]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/andrewhayden@chromium.org/422253002/1

[commit-bot: I haz the power, 2014-07-29 15:24:33]

Change committed as 286200

[waffles, 2014-07-29 16:23:37]

lgtm