[components/crash] Add crash client method to enable microdumps

[components/crash] Add crash client method to enable microdumps

Background context:
 - This CL is about breakpad *micro*dumps, not to be confused with
   minidumps (see crbug.com/410294 for details and design doc).
 - Breakpad microdumps are, before and after this CL, enabled only
   for Android.
 - At present state, the logic that decides whether microdumps should
   be enabled or not is hardcoded in breakpad_linux.cc. Such logic
   today enables breakpad only when unwind tables are stripped out.
   So far so good as it was the only intended use case.

New use case which justifies this CL:
At this stage of the project, Android WebView is also going to get
microdumps. Conversely to what happens in Chrome, however, WebView
needs microdumps to be always enabled. The rationale of this choice
is: WebView can not take advantage of the regular minidump uploader
and microdumps are going to represent the only form of crash reporting.

From the crash/ code perspective, this invalidates the assumption that
microdumps can just be enabled when NO_UNWIND_TABLES == 1 and requires
the introduction of a more customizable logic.

Description of the change:
This CL is a minimal refactoring required to introduce such logic. It
adds a ShouldEnableBreakpadMicrodumps method in CrashReporterClient and
moves the NO_UNWIND_TABLES logic around.
The overall behavior of "when are microdumps enabled" is unchanged after
this CL.

BUG=410294, 456494
Committed: https://crrev.com/61b6a6a609434dc42082e5f59278eca17b2d9417
Cr-Commit-Position: refs/heads/master@{#315328}

[Primiano Tucci (use gerrit), 2015-02-07 14:53:29]

primiano@chromium.org changed reviewers:
+ jochen@chromium.org

[Primiano Tucci (use gerrit), 2015-02-07 14:53:29]

jochen, can I ask you a review on this very small refactoring?

This is required for crrev.com/902093003 (webview stuff)

Thanks

[jochen (gone - plz use gerrit), 2015-02-09 14:20:29]

lgtm

[Primiano Tucci (use gerrit), 2015-02-09 16:29:19]

The CQ bit was checked by primiano@chromium.org

[commit-bot: I haz the power, 2015-02-09 16:30:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/904213002/1

[commit-bot: I haz the power, 2015-02-09 17:17:38]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-09 17:18:28]

Patchset 1 (id:??) landed as
https://crrev.com/61b6a6a609434dc42082e5f59278eca17b2d9417
Cr-Commit-Position: refs/heads/master@{#315328}