Reland: [Cast] Consolidate plethora of GYP files into cast.gyp and cast_testing.gypi.

Reland: [Cast] Consolidate plethora of GYP files into cast.gyp and cast_testing.gypi.

Reland of r265481 (https://codereview.chromium.org/245893005/) with the
following fixes:

1. Re-introduce 'include_tests%' conditional.
2. Conditionally include all Cast utility app targets based on a new GYP
   variable: include_cast_utility_apps
3. Fixed compile errors exposed by landing r265481 on the tree.

Testing:

1. This change was tested by building on Linux:
   `build/gyp_chromium && ninja -C out/Debug All`
2. Confirmed absence of 'include_cast_utility_apps=1' in
   chromium.gyp_env will disable the Cast utility targets.
3. Ran utility apps to confirm the fixes.

R=hclam@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=265690

[miu, 2014-04-23 04:41:53]

hclam: PTAL at the diff between PS1 and PS2.  Patch set 1 is what I landed in
r265481, which passed the try bots and then broke all the bots in the tree. 
Patch set 2 are the changes I'm making to fix the problems.

[Alpha Left Google, 2014-04-23 18:10:17]

LGTM.

[miu, 2014-04-23 18:30:35]

Committed patchset #2 manually as r265690 (presubmit successful).